A couple of suggestions regarding the patch:

(1) I'd suggest leaving the first part of handle_range_longs intact, up to and including the "/* ilow and ihigh correct now; do istep */" block.  Then build out the three "if (!PyInt_Check(...)) ..." blocks below to include argument conversion.  I think the patch would look cleaner this way.

(2) Rather than using PyNumber_Long, I'd prefer an explicit check for, and call to, nb_int.  This is the behaviour that's used for the 'l' getargs format.  PyNumber_Long is considerably more complicated, and involves looking at __trunc__ and __long__;  so if you use PyNumber_Long you'll still end up with inconsistent behaviour between small and large arguments.