66 Valiant slant six radiator upgrade/swap

Not a silly question, as there are none of those. We all learn stuff about these cars by asking questions. No, an overflow tank is not required. My stock radiator had no tank, just an overflow tube that dripped on the ground as needed. I added the tank partly because I think it looks cool, partly because I didn't want to puke antifreeze on the shop floor, and partly because I have dogs - antifreeze is toxic to dogs and I didn't want to chance making one of them sick.

My car is a 3-speed, so I had no cause to mess with the tranny cooler at all. As far as I know, the fittings are standard.