00malibu

I have my girlfriends 2000 malibu 3.1 with 94k on it its been over heating alot and leaking oil everywhere from my experience over the years Ive seen that the intake manifold gaskets were the main cause of these symptoms. So with me being a mechanic I figured I would save her a good 900 bucks firestone said they would charge her and do it myself. Took it all apart put the new gaskets in and referred to google for the torque specs for the rocker arms. One way or another I recieved the wrong specs and ended up tightening all the bolts to 50!! ft/pnds smh (palm to face) Found out later that it was 10.3 ft/pnds I was down to my last 3 bolts when sure enough one of them just kept spinning. I went and bought helicoil and I already had a tap and die set got the 12x1.5 and tried to tap it but it doesn't seem to be working Im starting to think I should just buy a used head and go ahead and do both head gaskets while I'm in there. What do you guys think?