You'll need to use one of those that has a screw clamp on top and two arms to grab the coils on the springs. They're a major PITA, and you'll end up with some carpal (sp?) tunnel probably... I've always hated using that kind of compressor, but if the heads are on and you don't want to spring for new gaskets, I think that might be your best option.
On the other hand, could you make up a stud that you could screw into the rocker arm bolt hole and use one of those pivot-arm type of compressors? IDK if the small threads would handle the stress of that though.