If it were me I'd pull the entire block down and check the piston rings. You probably have some bad rings in there. If the block is honeable (meaning you won't have to bore it out) it'd replace ALL bearings and rings. Check the pistons just in case as well. Have the crank checked for wear and the rods too. Also have the head checked for evenness, you may need to have it decked. Head gasket too since it will have to be removed when the head is pulled.
Edit: actually. I've never done this before but have heard others mention it. Try a leakdown test. From what I have gathered that should help aid you in finding exactly what is leaking the compression.