I've done a few of these swaps, my YJ and another buddies yj and my dad's 75 cj5. All of them we used the 7120 4.0 head, 4.0l intake/ flex exhaust manifold, and a carburetor adapter from a guy named Mike Ehrmann. His number is 1-719-337-3977. The adapter cost $85 but was well worth every penny because of the ease of use. It is specifically for a motorcraft 2100/2150, which is what my friend and dad went with and I used the adapter along with another to install a DIY Junkyard TBI.
Now since my Dad's cj is close in years to yours, that means you'll have the 7/16" head bolts and the 4.0 head uses the 1/2" head bolts. On my dad's I drilled out the block and tapped them with my milwaukee magnetic steel hawg to get a perfectly placed 1/2 hole. On an old ford engine I used 1/2 to 7/16 spacer adapters which worked out nicely and should work on the 258 so no drilling needed. The summit part number is TFS-51400419
1989 YJ, (Soon to come: TBI 350, 4l60) np231 sye/wide chain/6 pinion planetary, D30 ARB & Ford 8.8 ARB 4.56, 31" rollers for now, bds 3.5" springs, 1" Boom Shackles.