1969 Dodge Dart Swinger 340

If it was me, I would consider an A500 out of a Dakota. You would have OD. Maybe run a 391 gear? Others will chime in. You can go 904 or 727 tranny.
Things to consider.
Tranny
Tranny lines
Radiator for lines
Convertor and bolts
Flex plate and bolts?
Dowell pins for engine to bellhousing Standard tranny are different (Don't use them)
Drive shaft?
Shifter and linkage. Column or floor?
Kickdown brackets and linkage.
Cross member and mount?
Probably missing something.