"I plan to keep the existing FI setup. Intake & exhaust mans stay. Intake is new for injection though I think exhaust is the same - uncertain - it has an exhaust manifold O2 sensor - uncertain if that existed on the carb setup."
IIRC, the last version of the 4.2, carb and all, and which went into the last CJs and YJ wranglers through 89 (I think?) had auto-metering carbs for altitude fuel mixture adjustment - so I am pretty sure there would have been some sort of O2 sensor. Based on todays EFI, it was pretty crude, but it worked - I drove my cj7 from the top of Mt Antero (14,000ft) and home to FL and back a number of times and I don't ever remember adjusting the carb - compared to either the Qjet or R2g I have now, it was a complex carb - albeit behind the times as most GMs had gone to TBI in the 80s. Jeep sorta skipped the TBI revolution and hung on to carbs for longer than most, then made the jump straight to EFI (possibly due to AMCs demise in the mid-80s and the Chrysler take-over in the late 80s).
I haven't messed with a jeep 4.2/4.0 straight six in quite some time...but 1995 would have been the MPI 4.0 HO (high output)....It was like 190 hp when it came out which really does put the early Renix 4.0 and carb 4.2 to shame...A lot of it was head design and multi port fuel injection - and as you want, that kept most of the classic low end torque of the I6, but gave some pep to to the higher end (albeit - its still not a 3000 rpm type motor for extended periods). Guessing some changes were made to the cam as well at the time to take advantage of better flow....
The old 4.2 was sorta diesel like...relatively low hp, small power band for gas engine, but lots of torque and it just runs even when mis-treated....
There was a willys wagon for sale around here 3 or so years ago that had a HO 4.0 swapped in - I wish i would have bought that one - it was out of my price range and I wasn't serious about buying yet...The ol wagons came with a flat head straight six (and I kind of wish I had bought one with an original style engine)...but those old L226 just don't have much function in todays driving. Anyway, for whatever reason, while those early L6s were oem, but the later AMC/Jeep straight sixes apparently are a PITA to fit in the engine bay and swap in.
It'll be fun to see your engine swap take place....There is part of me that debates just dropping the coin for a new sbc 350 crate engine for the wagon....old cars are fun, but more fun when they run like new.