Hotshoe36: I didn't think I would be asking anything "narrow" in asking folks for ideas on what engines might be simple, reasonably powerful, practically installable, somewhat retro or nostalgic in appearance, and relatively low weight!
Aren't we ALL looking for variants of this, with different individual degrees of emphasis on the various factors I mentioned???
You might be surprsied by some of the outcomes. For example, after I modified and sueprcharged my Chevy SSR's 5.3 liter (327 cubic inch) engine to 575 to 600 crank horsepower, AND regeared from 3.73 to 4.56, my gas mileage at 60 mph, on hilly Texas 4 lane highway is still OVER 20 mpg! And that's hauling 5100 pounds (includes the SSR, the blower, 1/2 tank gas, and me).
As for those LS series engines not ebing suitable for a work truck, are you aware that for several years now, ALL Chevy V8 pickup trucks use LS series engines variants? They are disgusied with different "initials" than "LS1" (like LM4, LQ, etc), but they are ALL LS series engines. Check it out.
If you read the history of the LS series, you will find that GM's target right from the beginning of design was a new TRUCK engine series that would be lighter and more powerful. The Corvette was merely the first usage because it is low volume, and GM did not want to install a brand new engine in its bread and butter vehicles (its trucks)the first year or two, until it had some actual "customer usage" experience with no unexopected failures. I'm not kidding. Read Will Handzel's book.
You guys on this board simultaneously "discovered" the almost perfect TRUCK - the AD series - when you discovered that neat Stovebolt engine. I like the Stovrebolt engine, but I LOVE the AD truck, and I keep imagining it with just a few mods that take out some old fashoned, unneeded weight (like 142 pounds of steel leaf springs for good ness sake!!) and add just a reasonable amount of engine power beyond what a Stovebolt can deliver and stay reliable.
I wouldn't make too many assumptions on where SLURP could end up. The AD truck is a wily old codger, full of surprises.

Jim G