[jdean]

based on the age of those 1971 heads. I think it was 1972 when most U.S. car mfg. went to hardened seats. But if your heads were late '71, might be ok.

I would recommend taking them to a reputable shop and asking them. Machinists with experience can tell if the seats are hardened.

C6 is not a bad choice on these, since it can take more torque without breaking than most manual trannys that come stock.

Good luck on the build. In your area, I'm sure it will be unusual to be sporting a 6-7 liter engine.