So, I did a search and didn't really find any answers that really answered what I am looking for.

What are the differences between Series 1 L 27 and L67 engines?
and what are the differences between Series 2 L 36 and L67 engines?

can a L 27 / L 36 block and internals be used in an L 67? ( Series matching, of course )

I know the upper half is way way different, I am mainly just wondering about the internals and if they would hold up to a boosted application if just the block and internals were used.

I have had a few people ask me about this lately and I myself would like to know for %100 sure.

Thanks.

Counting the BLOCK and rotating assembly only, the only thing the same is the crank and block. The rods, wrist pins, and pistons are all different. How they'll hold up over time is the debate. If you plan to mod, don't mix/match.

This applies to both Series 1 and Series 2. All L67'* use stronger rods, different pistons (hardened, and with a different ring configuration designed to reduce chipping under detonation), and a better wrist pin (fully sleeved, not floating).

When my L67 crank got er uh..accidentally damaged, I checked into the L36 alternative.

Performance Vendors said for long term daily driver, do not do it.
Local performance enthusiasts that had the L36 in their supercharged cars said do not do it.

Overall the resounding majority said not to mix and match. L67 was built that way for a specific reason.

Then looking for motors around here showed me that the L36 was in higher demand because of the UIM failure than the L67 and the L67 was priced lower.

Series 1 L67s, in addition to what Bill said above, also have a coating on the crown of the piston...presumably to insulate the piston, and protect it from direct preignition.