Slant six info

I think the blocks will all bolt up the same. The engine brackets changed to spools in the 1970's, but just re-use your original brackets. As mentioned, get the spacer ring to put in the crank register if a later crank (1968+ or so). A member here (Charlie_S or such) makes and sells them ~$20.

The early 70's blocks are supposed to be strongest, but check slantsix.org. Original for 1965 is one w/ 3 staggered core plugs ("freeze" plugs). In the mid 1970's they changed to a cast crank. Some racers prefer it since lighter and they say it is still strong enough even for a turbo or nitrous. The slant's lower end is akin to the 426 Hemi and even shares some parts.

They dropped the spark plug tubes ~1980's. Those are called "peanut heads". Other than less oil leak concerns, I don't think any advantages. A big downside is you must then remove the head to replace lifters. If you want to use one of those heads, I recall some changes are required for oiling, especially if you use the hydraulic lifters.

Finally, there was an aluminum block in early cars, which was the original intent for the slant, but I think it was dropped before 1965. You can't get head gaskets for those and most were corroded beyond repair. Otherwise, one would be cool.