I got everything removed from the block today (except camshaft bearings). Looks like the rod bearings for #5 cylinder failed which was causing the rod knock that the previous owner had mentioned.

The main journals measured 2.3 inches and the rod journals measured 2 inches. The pistons/cylinders measured 4 inches.

Upper main bearings were stamped:
57653 GMM420 293G5 (2x)
57653 GMM420 293J5 (2x)
GMMA 57868 287HH5

Lower main bearings were stamped:
57653 GMM420 258N5 (4x)
GMMA 57868 180A5 (the A was upside down)

Rod bearings were stamped:
57734 GMM500 280N5 (4x)
57734 GMM500 280J5 (3x)
57734 GMM500 280J3 (1x)
57734 GMM500 288A5 (1x)
57734 GMM500 280B5 (1x)
57734 GMM500 253E5 (1x)
57734 GMM500 287X5(1x)
57734 GMM500 280A5 (1x) (the A was upside down)
57734 GMM500 280L5 (1x)
unknown trashed bearings (2x)

Crankshaft was stamped:
4577 (I didn't notice another number anywhere)

Camshaft was stamped:
K1 GM84 2798

Pistons were stamped:
3796494













bad rod bearings (#5)

crankshaft wear from bad bearings (#5)

rod wear from bad bearings (#5)


#2 cylinder

#4 cylinder

#6 cylinder

#8 cylinder

#1 cylinder

#3 cylinder

#5 cylinder

#7 cylinder