If they are in good shape use them. A 74 should have a manifold type condenser which is more efficient. Make sure you run a shroud and good clutch fan. Using 134 you only need 75% of the R12 charge. A lot of people think more gas = more cooling. I slowly add 134 until the low side hose at the firewall starts to get really cold. I'm in FL and on a hot 90* day my high side pressure runs 250.
