I think it is possible to carb a 4.0 and run a duraspark ignition on it as well. If the oil pump drive shaft is the same on the 4.0 as the distributor shaft on the 2.8, you should be able to run the 4.0 dist. gear on the 2.8 dist. and put it in the 4.0. Most likely it wont be the same as the 2.8 but rather the 2.9 which in this case, will not work, Ive tried and I scrapped a 2.8 duraspark because of it.
If it works, than that takes care of the ignition. I think it would be fairly easy to fab up a new plenum with mounting for a few weber side-drafts or even hash one out for a holley or so. I think the 4.0 could be a healthy little carbed engine if built right with bigger valves/port job, huge cam, and hi compression. Its way simpler to run those upgrades on a carberated engine. Im already planning a way for a carb/duraspark conversion on a 2.9.

 

Same as the 2.9, just got back from the junk yard. Didnt somebody make a dual-point dist for the 2.9? I remember a website that had it on there but I cant find it now.
I did manage to score 6 "brown top" injectors from 2 turbo coupes at the junk yard, total $6.53.