On my 65, its ~27.5" between frame rails. Battery is in the trunk so i have no tray to interfere and a couple things had to be relocated, but the biggest radiator i can get to drop between the frame rails is a 26" wide.
This could be a fun job. Cut you out a piece of cardboard and get a tape measure and make the darn thing fit. Good conversation piece with the buddies.
NO. I have a Summit 31x19 crossflow originally out of my '89 GT and its huge. I also have my stock '68 radiator out and could take comparison pictures if you want. I know the '69s had a bigger rad, but the size differential is so large that its not really worth "making" it fit.