you dont have to pull the head to change valve stem seals.. you need an air compressor and a compression test kit. what you do is thread in the compression tester hose (into spark plug hole) and you introduce air into the cylinder. be aware that it will turn the engine a few degrees. the air will keap the valve closed (seated in the valve seat) while you remove the spring and replace the seals. it sounds like maybe your rings are screwed.. that is alot of oil to be losing. you are sure there are no leaks??? the block and head are dry?? you might as well do a compression test on all four just be sure that its worth the effort to replace just the valve stem seals
on the exhaust, i know those bolts are bastard to start because there is tension on the exhaust..so whever did the oil pan last or exhaust work probably said fuck it, because usually they cross thread in.