Frankly I'd focus on the bottom end and worry about the top end stuff later, even though you have a head in front of you that I'm sure you'd like to play with. Personally, I wouldn't trust 20 psi to any block guard... aftermarket sleeves definately. Since you have a head you can poke around for a b18 or b20 bottom end in any condition, send it in to GE or whoever, get back a fresh clean block.