I can't comment on the early firewall rib as a '74 doesn't have it.
My 80 series booster bolted straight onto my '74 and '77 boosters with no spacers (only minor push rod adjustment). I was able to fit in the 80 series booster without a spacer, but I'd recommend using one for an easier fit.
My 80 series booster bolted straight onto my '74 and '77 boosters with no spacers (only minor push rod adjustment). I was able to fit in the 80 series booster without a spacer, but I'd recommend using one for an easier fit.