Factory mounted them solid on right side and used rubber well nuts on the drivers side.

Check out the grommets used on a Lexus GX 470 radiator, any year. You would have to weld a short piece of tubing to the mounting flange of the radiator to put the grommets in and they are big, like 1.75" in dia. probably, but 4 will certainly do the job, it's what I plan on doing with mine. There are cheaper ways but they're super slick and ready to go.

I'm trying to figure out how to mount my C&R in my 69 firebird too. They must use the term "bolt in" pretty loosely I think. None of the bolt holes seem to line up with holes in the core support. I think I am going to have to cut and modify the core support to open it up so the rad sees all the air it needs. Mine came with 2 sets of the rubber nuts and bolts. Did you get yours mounted yet?

you will have to line up the holes that do then re-drill the others.

I used these rubber mounts from mcmaster-carr

http://www.mcmaster.com/#vibration-d...mounts/=sv9thk

I was told that NAPA sells the well nuts.