I put a bigger one on my 69. Don't remember specifics. Offhand I think it was a 12si (the one with the plastic fan), around 90 Amp, made for an 80's Camaro. Don't know if I HAD to, but I replaced some of the wiring with bigger gauge wires, since I was rewiring everything anyway. Moved the junction/splice from on top of the engine to a junction block on the firewall.

If you need, I can dig out the specifics on which alternator it was.