I had my 1990 4.2 with a two-barrel carburetor converted, and it went extremely well. At the time, Mopar sold a kit to make this change but it is no longer available. It was worth it regardless of cost as the 1990 4.2 vacuum and emissions systems were extremely complicated and unreliable with many aging parts that were no longer available. In California, it was getting very costly to pass the Smog testing.
All has been good since the conversion, including one engine change not related to Fuel Injection. The entire system moved right onto the new 4.2L long block.
The conversion included a computer control that turns the fuel delivery system essentially into a 1994 4.0, except, the engine is still a 4.2.
If I had it to do over, I'd do it in a flash. I only regret not doing it sooner.