slant 6 auto(904) to 4 speed help

Measure the bearing retainer on the front of the transmission. If it 4.35 inches you can use the 3 speed bellhousing if it is drilled for the 833 bolt pattern (dual pattern). Most were from '68 on. Make sure that the inner surface of the bearing retainer register hole hasn't been sandblasted or doesn't get that way. If it does, the transmission to crankshaft concentricity is out the window.