Depends what you mean by "64-bit capability". I would say it means 64-bit pointers, and that would require a 64-bit CPU, as well as a 64-bit OS. For example, DEC Alpha ran NT4, but had 32-bit pointers, so that combination was not true 64-bit. The same machine running VMS or OSF/1 (Tru64) has compilers that supported 64-bit pointers.
Size of a long is only defined as not being shorter than an int. It is not connected with the size of memory addressing, although in practice it is often the same.
All this is a good reason to use Perl instead, don't you think?