I have a similar type car with a Cad engine and TH400 and a 13 inch converter. Takes a 2500/3000 stall in these cars. the 10 inch converter can be done but one gets the smaller converter from a chev with the proper spline count to fit the TH400 and then changes the flywheel to one that has the smaller bolt pattern that bolts up the smaller converter. Takes $$$$$ to do this and is not a real advantage unless one is running comp eliminator or something...
I have tried most all of it and now do what is known to work..