'
Heads may be later but O# Casting Alloy SB's bring the CERV cars to mind.
Cerv-1 w/ Alloy 283 was likely an Alcoa O# Casting as pics of one a guy had in his Corvair at this link...
https://www.hagerty.com/media/automo...-into-corvair/
Cerv-2 program parts may better fit subject if you can find info/details?
The 1990 Cerv-3 Corvette was reportedly a Lotus built Alloy 350 so may fit uncommon Flat Crank piece of the puzzle?
A few questions;
How long did GM use O# Castings?
Was there leftover/unfinished 60's O# Alloy blocks available late 80's to supply Lotus?
Did GM still have Block Castings to make new Blocks 70's/80's w/ changes/modifications?
What specific GM Alloy SB's were Chaparral or other Racers using 60's/70's/80's?
Do the CGT4 CONV1 Castings help indicate timeline also is the Block w/ same #'s at this link a brother or perhaps someone previously seeking info on this same Subject Block...
https://www.camaros.net/threads/gm-a...-block.124075/
Any truth to the Military Alloy SB's mentioned in above link and what parts were they using?
Whether info correct or not, did you see this 2012 Camaros.net posting...
https://www.camaros.net/threads/alum...engine.214727/
Keep digging Jason, super interesting stuff and looking forward to what you figure out!
~ Pete
.