So I got myself a donor 4 bolt main block yesterday and tore it down getting it ready for the machine shop. Now I need to order my master rebuild kit from northern. Before I do, I'm a little confused. I pulled this block from a 79 Chevy bonanza, the casting number says this block was made in 1986 and up. Not too wierd. What's wierd is it has a 2 piece rear main, and it is an internally balanced engine (no weights on the flywheel) I thought that Chevy went to a one piece in 86 and the crank was externally balanced. I'm thinking I'm gonna just order a kit for an 84, unless there's something I need to know before I do. The casting number is 10066036. Made in Mexico. Has a solid cam. Didn't take a picture of the casting on the heads but they were 2.02" int and 1.6" exh. Just curious before I order the kit why this is a 2 piece internal balance engine.