I'm not sure that it is a real problem at all. There must be millions of 4WD's & trucks running around with quite severe angles in their prop-shafts & these do hundreds of thousands of km's without trouble. Intuitively, I guess that a "straight-through" setup would be optimal, but I suspect that the losses through a well arranged angled set of uni-joints would be in the order of fractions of a horsepower.

The most critical thing is to try to have the input & output shafts parallel, & to ensure that the 2 uni-joints are 180deg out of phase (this allows the cyclic variation in rotational speed through 1 angled uni to be exactly cancelled by the variation through the 2nd uni - assuming that the angles through each uni are the same).

My DRB has a Porsche G-50 box & the driveshafts are angled down about 10deg & forward about 5deg. Some of the early versions of this car have now done some serious mileage, & none (to my knowledge) have had any problems with the drive-shafts.

I hope that the above helps a bit.

Kind Regards,

Peter D.