1: I run the ford yellow injectors on my YJ. Im not sure if the TJ calls for more fuel. The ford ones are 19lb as well, but have a better spray pattern.
2: I would pull it apart just to check it out. The heads are crazy easy to disassemble. It also wouldn't hurt to check out the inside of the engine before going through all of the trouble of the swap. When you pull the head off, if everything looks good, I would just replace valve seals and use some grinding compound to clean up the seats. Other than that you should be good to go.
3: Usually a waste of time. Put it on ebay or cl and see if anyone will buy it.
4: Yes to the header and the TB. While you have it off you should port the back of the TB to match the size of the blade. There is a reduction after the blade that chokes it off a little. Also make sure the intake manifold matches the TB diameter. If not give it a little porting as well.
5: Not sure on the return line with crossing over of rails.
Hope this helps.
1992 YJ 2.5L
Engine Mods:4.0L TB, Ford Design III 19lb Injectors, Firepower Ignition System, Ford TBird Electric Fan, Pacesetter Header, Magnaflow Cat, Dynomax Super Turbo Exhaust
Suspension Mods:BDS 2" Lift, M.O.R.E. 5/8" HD Shackles, 1" Brown Dog MML
Other:LED Tails and Herculined