Welcome to Hett Enterprises of Marion, KS. This is a late model block with the large volume oil pump. You can use this in place of an engine that has the small volume oil pump but you will have to swap out the oil pump shaft that presses into the front of the block. Of a engine that spun a rod bearing.
Is an excellent block that has standard size cylinders. It has standard size cylinder bores and does not need bored oversized.
The main bearing holders are included. This is a genuine Shibaura block not a cheap Chinese knockoff which are junk!