Just switch the head and block and oil pan from the 2wd '91 into the '94. The engines are exactly the same, but the oil pans, plenums, wiring and ECUs are not. Don't make more hassle then you need. The intake plenum changed in '94 to a better setup, they went to sequential multiport fuel injection sometime between '91 and '94 ('93 I think) so the injectors will be different with different plugs and require a different ECU, and I think even the clutches and flywheels will be different.
I think your '91 2wd will be a 8 13/16" flywheel/clutch setup while the '94 4wd will be a 9 1/4" setup.
Again, save yourself a bunch of grief and just swap the block and head assembly into the '94 and change the oilpan (I could be wrong, but I think the oilpan on a 4wd is different than a 2wd which may also require changing the oil pickup).
Just an opinion.
edit for clarity...whoops....switch the oil pan from the '94 onto the '91.
Last edited by Fahrenheit 451; 05-19-2005 at 11:38 AM.