Shannon Briggs is out of the picture as he's still young at 43. Here are the list of HW's who are/were recently active and are around 50's Razor Ruddock - 51 y.o. Bert Cooper - 49 y.o. Billy Wright - 50 y.o. Hassan Chitsaz - 57 y.o. Ruddock and Cooper were HW contenders in their primes, Wright was punching bag in his prime, Chitsaz only had 3 pro fights till his 50s. I'd guess Ruddock would be 3-0, 3 KO against the other old guys.
Ruddock is terribly shot. Chitsaz is prime, so he wins this tournament. However, WBC #15 ranked Billy Wright might be a tough outsider as well.