Just use Silverfrost, g95 or gfortran. They're all free.
Build it as a F77 program. The main difference is that some of the vendor specific stuff in FIV is now standard in F77. These are things like opening and closing files, direct access files, getting command line parameters and random numbers. Characters are new but the rest of it is the same.
If you get any compilation problems, post them here and someone will be able to point you in the right direction.