IH stamp on 318 block

My Aussie 318 is an IH casting. It's from a late 70's sedan. Here they come with the factory heavy con rods, & I've been told are a heavy duty block with a thicker casting that can go 80thou over bore. Mines yet to be checked, it only has a small lip in the bore which is already 40 over. So hoping I can get another turn from it. Even 318's are getting silly expensive here, to the point you can get a good running LS and box for less than a junker 318! Little wonder people are moving away from Mopar powered Mopars!