I just double checked some part numbers on the B&M site. If you check part #20480, it fits TH350, TH375, TH400 & TH425. I think there *were* infact, TH400 with a different input shaft (as mentioned) in the early 60's. Don't hold me to this, but I believe they were compatible with the early *switch-pitch* converters.
As a related sidebar, in the 80's I had a friend with a budget 427 Chevelle drag car who ran a 10-inch junkyard Vega TH350 convertor in a TH400. I don't condone using stock Vega converters behind BBCs but it works! er, for a while anyway <grin>. It stalled around 3500 RPM for 2 seasons, then started getting looser in the middle of the third summer of racing. The cars slowed at that point too.
MV
