What started out as a question on how to secure a Penny-Farthing has evolved through significant peer review (see comments) into a broader discussion of really a comparison of competing security options to protect expensive bikes- Penny-Farthings or otherwise. So somebody interested in securing their expensive street or mountain bike could benefit from reading this article.
This solution has been significantly peer-reviewed and I've updated the answer to incorporate the useful feedback in the comments from @Michael, @Criggie, @DanielRHicks (from his comments in the "Question" section"). Thanks to all who took the time to contribute to improve the quality of the answer; I'm most obliged.
Security Design Plan:
The security is to prevent theft of the Penny-Farthing while garaged.
The security should not be able to be defeated with bolt cutters, but require advance tools like an Angle grinder which will be loud, attract attention and take increased time to defeat the security
Immobilize the bike in a way to prevent a thief disassembling the Penny-Farthing to defeat the fierce chain & shackle. ie: the thief can't remove the rear wheel fork, remove the front wheel and/or slide the chain off of the spine using disassembly techniques.
Once immobilized in such a way that a thief can't leave with enough parts to be useful through disassembly, chain the Penny-Farthing to a fixed object to prevent it being removed to a location the chain can be cut using an angle grinder or other heavy-duty tools.
Alternatives Bike Security Considered But Rejected:
U-Locks: After researching solutions, I saw too many pictures of these on the 'net being defeated by cutters. U-Locks were therefore quickly removed from consideration.
Standard Bike Chain: I tried using one of these, but the effective length of the chain is only 50% because the free end must be looped-back to the shackle. Although the Penny Farthing could be immobilized, there was insufficient slack to chain it to a fixed object. So a thief could throw it in the back of a van or truck and subject the chain to an angle grinder at their leisure without risk of getting caught.
Longer Non-Bike Chains: Bike chains are crazy expensive. But to be fair, they're pretty fierce and incorporate features to defeat cutters and leverage attacks. For the sake of completeness, I investigated potentially purchasing just a long length of commercial chain. However, it was expensive and no where near as tough as the bike chains.
Hybrids: Producing a solution from using different security types. The cost of these generally exceeded the cost of the ultimate winner, the "Kryptonite NEW YORK CINCH RING CHAIN 1213" which provided an integrated approach where the system was designed as a whole. So a hybrid system of separate lock types and chains tended to be more expensive and introduce weaknesses into the system as a whole.
Solution: The Cinch or "Noose" Chain:
This chosen solution below uses a single chain "Kryptonite NEW YORK CINCH RING CHAIN 1213" to achieve the security design goals. Could be used when cycling, but at 10.55 lbs (4.79 kgs), you'd need to be a pretty sturdy person to lug it around ;-)
After being unable to both render the bike inoperable AND secure it to a fixed object using a standard security chain, I discovered the "noose" chain. Its' genius is that instead of using one BIG loop to chain both ends to a shackle, it allows you to create a "noose" around the wheel & spine/frame while creating a SECOND loop around the fixed object giving you the maximum possible effective useful length of the security chain. And this solution is extensible to ANY type of bicycle.
On one end of the chain is a large round link that allows the free-end to be fed through it. Now there's more slack to wrap the chain around a fixed object and then join the shackle to it.
A few illustrative pictures on how specifically to secure a UDC Penny-Farthing follow. However, a cyclist who uses a "safety" bicycle can also immediately see the benefits of the noose chain.
The model of chain depicted in the solution is:
"Kryptonite New York 1213 12mm 120cm Bike Chain Lock With EVS4 Shackle"
Pass the the chain through the front wheel and then pass the free end through the big "circle" link on the chain's other end ABOVE the mount pegs on the spine of the Penny-Farthing to create a "noose" and cinch it tightly. Alternatively, one could "noose" through the front wheel & forks.
After "noosing" the front wheel to the spine/frame, run the free end of the chain around the fixed object. Ensure that you choke-up as much free slack between the cycle and the fixed object when joining the shackle: this prevents the thief from loosening the noose to slip it over the mount pegs. PLEASE NOTE: I know a movable ladder is not a great fixed object and only used for illustrative purposes. I'm not going to show how I secure things on the Internet. I also have a cameras with motion detection ;-)
The Final System: Remark that the "noose" chain employs TWO loops ensuring you get the maximum effective chain length for your money!
This chain is HEAVY. So not really very portable unless you're The Hulk. However, when toodling with friends on our Penny-Farthings, we tend to take them into pub gardens and "stack" them together next to the table, so they're never really unattended. I really just use the "noose" chain for when it's garaged.
I accept that given enough time and opportunity, ANY bike can be stolen. I'm merely trying to increase the level of difficulty to stealing an expensive bicycle. Anyway, after ages of racking my brain trying to secure my Penny-Farthing, hopefully this saves others the same grief.
This is ONE solution; I'd be keen to hear how others have solved this problem!
About the Security Designer:
Although a Linux & Network Engineer now, I served formerly as a New York City Police Officer. So I have some insight into how naughty people behave (or rather "misbehave"). And I cycled in New York City, where if one leaves their bike insecure it will be gone in the proverbial "New York Minute". Indeed, that's why Kryptonite brands their fiercest locks "*New York". BTW, I've never had my bicycle stolen living in Gotham which I consider quite an achievement ;-)