904 converter missmatch

What year is your car? That would possibly explain why you're having problems. If your car (or the engine is a 67 and earlier) it takes the small converter hub. 68 and newer engines take a converter with a larger hub. Additionally, the converters will not interchange frpom pre-67 to post-68 because the spline count in the front pump is different. That would explain why your old converter fits the crankshaft but does not fit the new transmission. Hope this helps.