If you are really considering diesel, and have the patience to wait and the money for a new motor, the new 2.8 turbo diesel looks interesting. Roughly 40 hp less and 100 ft-lbs more completely stock, but if it's anything like other turbo diesel engines it can be cranked waaay up all while netting higher mpgs than the stock i5 could ever hope for.

 

Ok...I found something I might want to attempt. But need to know, if it will fit.
I measured the engine front to back, the width, the height at the rear from top to bottom of the rear oil pan, and the height at the front from top to bottom of oil pan
from fan hub (w/o fan blade) to flex plate [------33"--------]
width [------37"--------]
depth at rear top to bottom of oil pan 37"
depth at front top to bottom of oil pan 34"
Right at about 500lbs
These are pretty close, but approximately with a tape measure.

Any thoughts? I am ready to pull the trigger if it will work. GM motor, I'm purposely not saying the exact engine it is right now...because, I don't want the blah-blah-blah. But, I think it would be an awesome build.

 

Not trying to be secret. Ok, so here is the deal. I have in my hands 3, yes 3
Post-bankruptcy GM auction engines. You had to bid on a semi truck load of sometimes junk, but not always and you got what you got. Well, there was lots of stuff but, there were three 4.9liter V6 duramax turbo diesels all set-up with wire harnesses, Bosch ecm's, and ready to be bolted to 4l80e transmissions. So recently, the old 3.7L 5 cylinder seized, hmmm....is this the time to see what a V-6 duramax would have been like in an H3T. I don't know, I'm kicking it around.

 

Part it out and buy an Alpha. No headaches and likely cheaper.

 

Engine swaps aren't like the good ol days. The money and fabrication, engine tuning etc and never ending hassle is just not worth it. My money would spend on a short block to get it going then sell it and buy an Alpha if you absolutely gotta have the 5.3. There is not that much difference between them. Then use all the money I saved and the time I didn't waste to buy a go fast car since that seems to be what you are after.

It's a brick with wheels. Meant to go off road, not go fast.

 

I would agree. Save the money for other upgrades and you'll be much happier. A simple swap will save you thousands, imagine the money going towards other goodies. I will swap my 3.5 for a 3.7 when it goes.