273 302 318 340 build
I'd use the X heads, 302s might be good on a 340 if you port the sh** out of them and put in bigger valves lol. 273 adjustable rockers too, sounds like a nice traditional build with all the factory "good stuff"... really looking forward to how this turns out, best of luck! Should be a lot of fun and pretty bulletproof with all the factory parts.
EDIT: BTW I have a 1970 FSM I could copy the pages with the specs you need and send it to you? Let me know which ones you need...