I'm in a dispute with a local machine shop owner that rebuilt a short block for me from a 89 K1500 4wd truck. I finished the engine out and installed it. When I fired it up after priming everything of course I discovered it had a knock and the oil pressure dropped off to nothing when stopped at a light after warming up. I took it back to him and he checked it over after many go rounds I took him to court. He showed up with a piston with a screw mark in the top of it saying a screw worked it's way out of the throttle body butterfly and into the engine. Now this might explain the knock but not the loss of oil pressure. I asked if there was any head damage. He said he couldn't tell since he didn't remove the head he took the piston and rod out from underneath without pulling the engine. Is this possible? I don't see how he could have gotten it past the crank. If he removed the crank from underneath is there enough room to get the flywheel clear of the torque converter? Assuming he did get it out would he be able to get a new piston back in without cracking a ring? Is this really the best way for a professional shop to do this?
Needless to say after court I went to pick the truck up and it still had the knock and loss of oil pressure. He claimed he forgot to tighten the torque converter bolts, another time it was bolts on the 4wd were missing and it was banging. Now we're going back to court and I'd like to dispute what he said originally as I don't think what he described was possible. I should also mention when I took the throttle body off there weren't any screws missing nor could I tell where one had been replaced.
Thanks for your time and advice.

Mcgyver