Help with old film curl?

I have a cigar box full of 35mm B&W film shot in the 40's and 50's by my father - wonderful stuff. Some Army, some Germany, processed who knows where, taken with the good old Retina II. Early stuff of family, etc.
He rolled up each roll, uncut, and put them back into the original aluminum film cans (the ones with wonderfully colored tops). Nice way to store, but the curl is a killer. I actually took 3 rolls, wrapped them backwards around a paper towel core for 6 months, in long printfile sleeves. Took them off, and they immediately sprang back into a tenacious curl. I also tried washing for 5 min, drying per normal - no dice, it must be in the film base, which doesn't take on water.
I've thought about rolling them back into the cans backwards, but fear for scratching.
Any ideas?

The best advice I can give you is to live with it. Short of stressing the film to the point where you might cause some damage, there's not much you can do about it. I've seen a couple of very old (~50 years or so) films that became so brittle with age that they literally broke apart when I tried to load them onto reels for processing. If you must, use a glass negative carrier to hold them flat for printing.

With a glass negative carrier (for either optical printing with an enlarger, or a glass carrier for your scanner) you should not have any worries about making prints from extremely curled film, it will just be somewhat of a hassle to load into carrier.

Last spring, I had the identical problem with a box full of film (mostly Tri-X and Plus-X) that had been developed in 1964--1967, rolled tightly and wrapped in strips of paper for labeling, and then stored in the attic of a barn in Alabama for the intervening time. I needed to scan the negatives before my high school's 40th reunion, and there was no way that they would go gracefully into the negative holder for the scanner. (Some of these were 36-exposure rolls wrapped to a diameter of three-quarters of an inch.)

After trying the obvious---reverse winding, hanging with a weight, re-washing---I decided that I had nothing to lose, and placed a sample between two pieces of clean paper which I then sandwiched with scraps of mounting board and placed in a warm (about coffee-drinking temperature) mounting press overnight. I turned the press off, and let it sit. The next day, the negatives were, if anything, flatter than they had been in 1967, and to my surprise there was no detectable damage to the emulsion or base.

I found that the paper was unnecessary, and made up several "fixtures" consisting of narrow flaps of mounting board long enough to cover eight-frame strips of film, and hinged at one end to a larger mounting board scrap. After putting one strip of negatives under each flap, a tab of masking tape held the assembly together long enough to get it into the press. With several flaps, an entire roll could be processed at once.

Only modest heat is required (at least with 1960s-vintage film base) and I didn't lose or damage a single frame from some fifteen or twenty rolls. This might not work with older film bases, and all of the usual caveats apply: test on an inconsequential sample first, and don't risk anything truly valuable, as the negatives are irreplaceable. I was working with snapshots, mostly of high school football and basketball games, so there really wasn't anything much to risk. I think that if they had been family snapshots, I would have wrestled them into a glass-type negative carrier and at least made archival prints before trying to salvage the negatives.

I've used painter's tape (blue) to affix horribly curled negatives of similar vintage to some anti-newton glass for scanning. I would imagine you could do the same with a glass negative carrier for printing. The tape holds it firm but also peels off easily without causing damage.

Thanks to all for the replies. I like Greybeard's solution, as I do this with prints all the time. Yes, the film is older by at least a decade, in some cases two, but surely I can find a roll that is not too important, and maybe scan it first.