Henry McCoy in his blue-furred form as seen from the 70's to the late 90's, so 80's version, vs Ben Grimm as he was in the mid 80's, Byrne era, as that is pretty much the default Ben Grimm.
I think this is a tough call, because it would depend on the setting, but in general, if Grimm gets a grip on McCoy it is game over.
However, McCoy is fast, agile, and nimble. If McCoy can evade Grimm, can he do so long enough to wear him down? I an see McCoy winning this by pushing Grimm to exhaustion.
Beast can very little do to hurt Ben and Ben will eventually tear down a building or similar so that Beast's agility is counteracted.
There may be the occasional upset due to Beast somehow using the environment but otherwise it is Ben.