From what I am reading, there are 3 attested tandem drivetrains:
1) crossover drive, with timing chain on the left, and main crankset and drive chain on the rear right. This seems to be most common.
2) Crossover drive, but with the main crankset and drive chain in the front instead of the back. This uses a very long drive chain, but has lower frame flex and better chain line.
3) Right side drive, with the main crankset on the rear. Right side drive has low frame flex, low weight, and low width.
What seems to be missing is:
4) Right side drive, but with the main crankset in the front. This would seem to combine the width , weight, and flex advantage of right side drive, with the chainline advantage of front-crossover drive. However, I have never seen it.
I'm building a tandem with no front derailleur, And I'm concerned about frame flex and weight. I'm thinking about trying it. I will just use small sprockets for the sync chain and a larger sprocket for the front/drive chain. Will it work? Anyone ever seen this done? Any problems?