Just do a valve spring change to a new set that fits your heads and works ok with your cam with your heads still on your motor. And install a new set of seals while you are at it..
Some guy's use the sparkplug air hose adapter, others use the "knot on the end", 3/16" rope way and still others use any of several hand-held valve spring compressors, either the little "clamp-like screw one" or a special cheap lever one that works off the studs...
Do a search and read up on this here b/c there are little tricks to using any methods!!!
One thing you do want to do is plug all the oil drain back holes so your motor doesn't swallow a keeper or two as you pop them out/off the retainers and valve stem grooves!! Saves a hassle, BIG TIME, imho!!!