16" diameter is what I used. Wiring it with relays is a good idea. The temperature adjusting module has a relay in it, so if you just use a sensor in the radiator you might want to use a relay. Alan Horvath's site is a good overview of how and why relays are good.

Pulling the top radiator shroud/hood latch panel is easy, just remove the bolts around the edges.

'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi