this project is awesome. i know you are extending your wheelbase, but out of curiosity, how much driveshaft length is lost using the 231 doubler you are doing?
With the one I am using lost is 7 7/8 inches. It comes with a clocking ring, if you clock it to where you want it and then drill out the clocking holes you can leave the ring out and save 5/8 of an inch so you lose less. I have a four cylinder so I thought about moving the engine forward. If you do that you can pretty much not lose anything. Alot of people do the doubler to a flipped dana 300 and then you are shorter than a stock drivetrain without the SYE. I already had the 2 231s so that's why I went that way.