I have a 1984 k20 4x4 6.2 diesel engine. I need to replace the main crankshaft bearings. I can't tell what size bearings are. On the bearing shows a stamp GM below that is a A-200 on all of the bearings. I went to the dealer and the part number is stamp on the bearing. Thinking it's a aftermarket bearing. Anybody have a idea of who's it might be or size?