The aluminum block I'm looking at is an LH6

 

I'm eyeballing an LH6 as well. It's an '05 with 118K miles. Nothing wrong with it. Been checking out some options for a build (want to build a 650hp turbo-aspirated for my Silverado), and my budget for the engine and trans is $7500. I'd like to keep the engine build to under $4500 total. So, chasing an LS isn't likely.

How are these LH6's? Stout enough to handle 650hp?

 

I don't see why they wouldn't be. I didn't get mine, because we replaced it with a brand new GM engine. GM has a $2500 core charge! They got it back.

 

The year/model of this engine has the active fuel management system, which uses solenoids to open the exhaust and cut cylinders when cruising. I am pretty sure I'd get rid of that system, so I'm also wondering whether that's a serious issue, or whether that system can be easily removed/disabled?

 

Yes DOD (AFM) can be deleted.

 

I'd do aluminum.