Motor Swap

I feel for you. I got a water jacket crack between the "core plugs" in my 1965 383 block long ago from freezing. I was flushing the system and drained, but neglected to remove the block drain plugs.

I bought the special adapter ring for the torque converter from Charlie_S here for ~$20. Might be the same part for slant & small block. I recall the year the torque converter snout diameter changed was ~1968. The other way to keep your early tranny is to swap both the torque converter and input shaft from a later tranny. Most who do that have the 1965- shift-cable tranny and don't want to fool with the shifter. For you, a later tranny should fit directly.

Look at the 1981 distributor innards. If it has the same coil pickup w/ reluctor teeth as 1970's Mopars, you can use it directly w/ a GM HEI (8-pin type is best). Search photos on rockauto and Google Images. In the early 1980's, Mopar switched to Hall-effect pickups that won't work. My 1982 Aries had that, but was also a new 4 cyl engine.