Early slant 6 Four speed bellhousing

Currently running with three speed now. Would never go back to 3 speed but if I did I would already have the bellhousing that was removed with the trans.

I just happen to have the 4 speed and shifter laying around. Cheapest way to install I think is to buy early 4 speed bellhousing and reuse my flywheel, clutch, fork, and dust shield on the early 4 speed bellhousing.

The later dual pattern bell housing would need an adapted ring for input bearing retainer and possibly a bigger flywheel, clutch and fork I think?

Going to have to research the difference on the early bellhousing 64 to 66. Definately want one that I can reuse the 3 speed parts listed above on if possible.