You might want to look into rebuilt heads from Adsit. The prices seem reasonable, and everthing is either new or rebuilt. Things to replace include lifters (especially if they're hydraulic), valve stem seals, grind valve faces and seats, replace weak springs, rocker arm bearings, camshafts (check lobes for wear), cam sprockets. Pretty much anything that moves. A shop will be able to pressure test the head or magnaflux it to check for cracks. Make sure the face of the head is flat, because any waves or bumps will result in a poor seal. Check the timing chain for stretch or general wear while you're at it.