I grew up in a GM/Mopar family so I a familiar with the pros, and cons, of the lines, at least from the 70's to the 90's. For Mopars, we joked about 'Dodge RUST Red' because of their horrible undercoating and propensity to rust, especially on the bottom, after a couple winters in the Midwest. With GM's, we told people that they were designed to leak oil because it seems like every GM engine ends up springing a leak somewhere. You just top off every couple months and, if you're 'lucky', you only need to change the filter at interval.
But we loved them. As I got older, I came to love most all cars(except Ford, the one Ford I had I put Mazda parts on because it'd 'run better', lol).
But I digress. I love the Iron Dukes. They were the first engines I worked on internally and it was an Iron Duke that I did my first rebuild on. I've run into the timing issue, I had an S10 with less than 70k on it that threw the chain. I was astonished because chains are supposed to be, typically, 'life of the vehicle', assuming 200k. I chalked it up to 'mass production fluke' but if what you're saying is true, I'm amazed I haven't run into more timing issues with them.
I was honestly thinking of pulling a 4 or 6 out of an S10, the problem being that I would want the transmission(assuming 5spd) and, likley, the transfer case(assuming I can get a 4x4 with a 4cyl). Although, as I understand, the 2.8's(truck geared) don't push much more in the way of torque and I assume it wouldn't need much in the way of reinforcement and the space needed should be 'negligible'.
I'm loathe to put a car engine into it as I want to make a 'Jeep Light' out of it, which brings me to the possibility of the Mopar Duke. But if you're saying it was weak on hwy, I don't know. My biggest complaint with the engine now is twofold:
1. It feels like a lawnmower on the road
2. I worry about over-stressing it as a ranch vehicle(off-road and light towing/pulling).
I would love to return to a carbed setup though, I grew up working on pre 80's vehicles. My dad and I built an old 76 Trans from the frame up and tossed a blown, bored 464 in there with a 4spd knucklebuster. It was beautiful. I loved that you could get some hp or torque gain with a flathead screwdriver, lol.
You're probably right that it would be a safer and easier prospect to pull a 6(or beefier 4) from a similar platform such as another Chevy/Geo Tracker or a Sidekick. I would imagine the mounting is fairly straightforward since the platform was designed for those engines and I'd think that the drivetrain, tranny, case and shafts, would be 'virtually' interchangeable reducing the need for fabricated/forged parts.
What I want is a little more torque for utility and preferably some better gearing/banding for the road.