Hello everyone, I'm new to the forum and wanted to say thanks in advance for all the help/advice.... Well the mains/rod bearings are nocking horribly in o6 Sierra 1500 z71 5.3 l. It has aluminum block and heads. Engine vin# b if it helps. It has 215,000 mi.on it so I'm completely rebuilding it. I wanna take my time and do it right so I'm planning on dropping in a cheep junk yard engine in it just to get me by.. My question is when I'm looking for my temporary engine will any 5.3l from gmc or chevy work? does it have to have a aluminum block or can it be iron.. Does the vin# matter. It's an everyday driver and I don't have the money to just buy a new one and I'm not about to rely on a junk motor for very long . Thanks again..