I use Harbour extensively to compile summer '87 code. As Ton Hu points out some modifications will be required, but if the summer '87 program is well written the conversion is quite straightforward, and the resulting executable, though much larger than the '87 equivalent runs MUCH faster, behaves better under current Windows versions (no cpu hogging) and gives long file name support, better error reporting and a lot of other enhancements.
I also run summer '87 programs on 64 bit Win 7, but only in virtual XP mode, which works well and enables you to create a shortcut on the Win 7 desktop which automatically invokes the 16 bit XP client to run the app very seamlessly. However this is only available on Win 7 Pro or above and requires a processor which supports hardware virtualization and lots of memory.
Ton Hu pointed me at Harbour years ago and I have never regretted it. There is a bit of a learning curve, but it is worth it.
Jock