So my all original 72 has a replacement engine block. What to do?

[PGG]

So I bought my 72 K5 Blazer 4x4 as an all original truck other then repaint in its original color before I got it.
Turns out the engine block is a 77-78.

So do I rebuild it with?

A. Build with this 77-78 4 bolt main block since I have it? Its standard bore.
B. Put in a new LT1 replacement and TH700 tranny?
C. Find a 72 4 bolt main casting and keep it as close as I can?
D. Buy a new warranted replacement?
E. Just F it and put a big block in it with 500HP?

I am leaning towards option C but no idea how hard that block would be to find and I feel like there is little upside to doing that value wise as I wont lie if/when I sell it anyway.

Thanks PG

PS, yes I am butt hurt if that matters I thought it was the original engine and there is no real going back.