So what does "cross flow" mean in terms of radiators anyway?
Fox body radiators are generally larger than the classics. I'm sure you could get one in there, but you'd probably need to build custom brackets, etc. Also keep an eye on the radiator hose attachment points. I seem to remember that you early guys have weird hose placement.
Cross flow refers to the waters path through the radiator, to the tanks. Water takes the path of least resistance, so staggering the intake port & return ports on different sides of the tanks(crossflow), makes the radiator more efficent, or in the example of the origional style rads( intake & return on the same side) less efficent.
Sometimes crossflow is used to describe rads with the tanks on each side, hense cross flow, as the Fox body rad is. Though the ports are still staggered.
Remember the girl in high school with the really big braces?
Well that's what your '65 is going to look like. Or maybe the Cheshire cat. Yeah that's it.
Measure the width of the '91 radiator, and then measure the width of the radiator cowl.
Can you?...Of course you can! Do you want to go to all the work?... measure it, then you tell me.
I agree with Runt. Its more not exactly a matter of can, more a matter of should. The radiator wont fit the core support with a stock setup, you will have to modify it. If you do a search on the forum you should find a thread from about 2 months ago on this very topic.
I actually found myself in the position of having to use a Fox crossflow radiator in my '65 last spring. First day at the track after a long winter, a poorly-timed downshift, a broken motor mount, and fan contact with the radiator (and of course I drove the track car to the track)... Long story. Anyway, the local parts store was scarce on radiators for 40-year old cars, but had a couple of Fox Mustang rads in stock. I took one and strapped it in with big nylon tiedown straps, hooked up a couple of flex hoses and made it home.
Bottom line - the Fox radiator fits, but not well. Much of the core is obscured by the rad support on the '65 and, of course, you'd have to come up with your own mounts (unless you want to use my cargo strap idea) It's thin enough to fit pretty well, and the height is about right - the width is way out of whack, though.
There are certainly better alternatives for a '65 (unless you find yourself stranded at a track with a broken radiator and no way home, that is)...
Thanks for all your input, the only reason I was looking into it is, the guy I got the motor from also gave me an aluminum Be-Cool. I was just looking if it would work or if I should sell it and buy the correct one, which I don't have a problem with.