Thanks, Chiphead. We had the 261 here, the ring gear is the same as the V8 and 250, 168 tooth, but the bolt pattern of the crank bolts is different. So no way to use one in the other. But I got no info in GMC. If some are 4 bolts, them the GMCs are different from both the 261 and the 250. As for the 235 and the 261, I've already changed one for the other, no problem. Only diferrence is in the clutch and starter ring, they both have the same bolt pattern in the crank.
