Scott: When I bought my machine it had a 390 FE in front of the small shaft top loader. After three months the engine lost a wrist pin retainer
which made a small gouge in the block. Instead of sleeving the block I decided to go with a new Shelby motor. While the original top loader worked just fine, I decided the nasty new motor needed a stronger (31-spline) top loader, just in case. I also beefed up the suspension, adding Watts linkage, etc. The 28-spline version will work just fine with a less powerful engine. Lots of 390 FE parts available as well.
Rich