I would like to update my previous post.
I recently did the "Junkyard TBI" conversion. If one word could describe all my thoughts on this it would be "awesome".
The whole process took less than 8 hours of my life, and cost me about $100 dollars.
I went to the junkyard and asked for a price for all the engine control electronics off a 1993 S-10 pickup, including the harness, throttle body, and ECM. The guy told me $100. I ended up trading him for the old 4.2 head, exhaust manifold and valve cover, which I removed during my 4.0 head swap.
Since the S-10 had a newer ECU, I stopped at a 1990 Astro van on my way out, and grabbed the ECM from it, along with 2 feet of harness.
On the way home, I stopped at the auto parts store and purchased a TBI rebuild kit, 14 PSI electric fuel pump, an o2 sensor, some wire, heat shrink, wire loom and a fuel filter, all for $92.
I went home, and did some internet research from binderbench.com and jeepforum.com on which wire in the harness goes to which sensor and made my own harness in a little over 3 hours.
The thing installed in just a couple hours and works great.
I had a very nice Weber on before, which worked pretty well, but this conversion is SO EASY, and now the Jeep starts with one quick turn of the key. There is no more sputtering on hills or flooding.
One thing to note, is that I did not use the electronic spark control. I used the "EST high reference" wire from the ECM to connect to my tach lead on the HEI distributor, and connected the "switched 12V" to the hot side of the HEI and that was it for pulse reference.
The great thing here, is that all GM TBI systems use the same color wires to the sensors, so making the harness is a breeze.
I would highly encourage anyone to do this and eliminate carbs all together.
For people who are intimidated by a little soldering and wiring, Howell has this conversion with all rebuilt parts and a pre-assembled harness for around $1000. I spent a four hours and did it for only $100 ($200, if you don't have anything to trade to the junkyard).
There is plenty of research material on how to do this available for free on the internet (google search Jeep TBI swap).