Re: 4.0L swap
Oh, Oh!! I've started a trend! (Yikes.) My 1973 J-4000 has a 1989 non-H.O. 4.0L in it. With mine the manifold is the same size as the 258ci I-6, just shaped differently. My brake booster is actually smaller than your Wagoneer's! I used the factory mounts for a 258 in mine. They bolted right to the 4.0. (I assume you used the mounts from the 4.0L donor?) Also, I did my engine frame "arm" mount like AMC did, with one difference: I put the steel plates lower on the arms than factory. By the way, the 4.0 is actually more narrow than the 258, so it can sit lower in the engine bay.
I assume you have an auto transmission. (I used a manual.) Hopefully, you won't have to relocate the crossmember. (I had to.) If you do have to ditch the booster, look for one off a newer model ('94 or newer) Dodge Ram 2500 or 3500 with a diesel. The power brake booster is the POWER STEERING PUMP!! (Yeah, amazed me too.) Just an idea.....