After switching the fork on a road bike I noticed that the brake pads could no longer be adjusted to sit properly on the rim but would sit too low even in the topmost position. I encountered the problem with Shimano 105-style brakes. Obviously brakes exist with short and long arms and I had to switch to brakes that have shorter arms. Are there any standards for the arm length or, equivalently, the distance between the bolt holding the brake and the rim?
Reach is the distance between the center of the brake bolt and the middle of the brake shoe. Generally, brakes are sold with a range of reach (usually written on the brake; this is because you have some adjustment with the pads), like 40 mm - 50 mm or whatever and are termed as short, normal, long and extra long reach (but the actual reach lengths vary based on the manufacturer and time period of manufacturing, so you need to look at the range of reach for the particular brake you're using; for example, a long reach brake today may have been a normal reach brake in the 1960s). People also use drop bolts to use shorter reach brakes when longer reach brakes are required.
Most brakes are probably 40-50 mm ish reach these days, though you need to check the particular brakes you're working with.
To measure the reach needed, take the wheel (ideally, without a tire), and remove the existing brake. Then, use a ruler to measure from the center of the brake hole to the center of where the brake should hit the outside of the rim. If this is 45 mm, pick a brake such that the reach range contains 45 mm (e.g. a 40-50 mm reach brake).
Sounds to me like your original brake calipers are not suitable for your new front fork, being a bit too long.
There are not specific standard lengths, but there are standardish sizes spanned where the brake reaches 32-44mm or 40-50mm. You probably want one size shorter than you have now
Possible solutions: * You could possibly file the brake calipers, but depends how much meat you'd have to remove. Not recommended, and not at all if its more than a millimetre or two to remove.
Offset brake pads - these hold the pad a few mm above or below the mounting. Downside, rotational forces tend to push these around. Poor patch to fix a problem
Offset the brake mount on the fork - again not a great idea. Brakes are important. However some people have used droppers to mount 650 wheels on a 700 fork, where "longer brakes" just aren't going to work.
Buy a new/replacement front caliper. This is what I'd do. I upgraded some single pivots to cheap dual pivots for a cost of $40 for both. Only Tektro level though, but still better and lighter than the original RSX single pivots.
Do please let us know what you end up doing, and what works for you.