Swap 904 to 727?

Maybe I missed something but if you're running a 318, why not just rebuild the 904? A simple refresh from a local transmission shop (if you're not up to the job yourself) wouldn't be too costly, the 904 is quite a bit lighter, requires less gasoline energy to spin and will save you the hassle of worrying about driveshaft shortening, yokes, etc.

With my Magnum 5.9 swap (from a 318 originally) I opted to have the bands and clutches upgraded, added a mild shift kit and a deeper pan. It's not going to hold up to a screaming boosted engine but likely more than strong enough for a mild Magnum...certainly enough for a 318.

Just a thought...