66 Valiant slant six radiator upgrade/swap

It's very tight clearance so the radiator would have to be pulled to remove the fan now. I learned this the hard way

Go and check your engine mounts, or you will learn the hard (and expensive) way that when the engine mounts get flabby, sooner or later the fan eats the rad. These ones won't ever fail; the compressed-cow-poo parts store ones from China or India will.

trying to gain some clearance with a smaller spacer

Good idea. Lookit this for some options.