I recall reading elsewhere that the OEM LS blocks are no longer manufactured, so the best bet is to try find a decent used block. Outside of that, what other OEM blocks plop into a F-body fairly easily if not a LS-based design? Late model LTs? The only other options are aftermarket blocks like those from Dart?

 

Any of the Gen III/IV stuff will fit with minimal concerns, though there are obviously some differences with accessories and external engine parts.

 

What I mean is, if OEM Gen3/4 blocks are awol, then we're limited to aftermarket or a bigger project w Gen5+?

 

Not all Gen III/IV blocks are gone. Active GM part number 19435098 is an LS3 crate engine (of course, this is a complete engine and not just the block, but it's available brand new - not sure if you can get just the block separate).

 

Assuming you currently have a gen 3 LS I would find a decent gen 3 6.0 iron block and rebuild it from top to bottom. Yes it will add some weight to the car but more cubes compared to a LS1/LS6.
It will bolt right in and with ECM tuning should run great.

 

Wiring changes aside, yes, a gen v will drop right in.

 

I can throw a rock and hit a Gen III LS Engine forsale so what are you trying to do here..