32 B4 rear seal missing

[my4dv8]

We sent our bare 32 B4 block in for crack examination and dip stripping to an engine restoration shop . the guy forgot to remove the aluminium seal thing (what is the correct name) So where do we start looking for the now dissolved part?
The block was not the best as it had been previously sleeved , and the deck surface was somewhat pitted . We plan to do an OHV conversion . But these blocks are getting harder to find . Better would be nicer. Was told on initial inspection it was crack free.