Your crank if drilled for only 1 dowel is the 6 counter weight unit. Some of the earliest ones are forged. It will also have 7/16 bolts. See if there is enough room on the flange to go to 1/2 bolts.
You never said your cam specs.
I think you will have better luck with a 168 flexplate for convertors to bolt up. Seems like the TH350/ 700 r4 convertors use a larger bolt pattern only on the larger flexplate.
If so, you will need to drill your block for the 3rd or offset bolt hole for starter.
I like the single exhaust setups.
Cleaner at rear of vehicle
Quieter
Run it split for a few feet before joining
easier to route thru vehicle
