The casting number was used on a lot of motors....including 2bbl trucks. Look on the pad that is just in front of the passenger cylinder head...look for a two letter code that is stamped, not cast.

The windage tray bolts are factory on some motors including a DZ motor out of a Z/28 and a 70 LT1. The pop up pistons are also a plus. However, these could have been added. In the early 70's, a new Z/28 partial engine assy was about $400 at the dealers. If you have a forged crank, the crank is worth more than that now.

Your motor could be either a 3" stroke or a 3.48" stroke motor....it is in such corroded shape that it probably will not turn over so you can measure the stroke.

Get the letter code....unfortunately, some replacement engines did not have a letter code stamped on the pad......