It is going to be just like rebuilding a 2.6, except for the carb part.

In general, it is going to expensive. Depening on how much you can do, prices in your area for machine work and parts, plus how much work (machinging, parts ect) you decide upon, I would not think it is possible for less than $1500. It will probably be closer to $2000.

That said, it maybe time for you to a) get a newer Trooper or b) revist your current engine (a compression test will tell you way more than "My oil turns black" because oil is generally supposed to do that or c) look at finding a 2.6 to drop in there. There is a little bit of work to do and you can use your intake/carb on top of it, plus it will make a noticeable difference in power compared to the 2.3.

Good Luck,
Michael