A FE block motor can be done, but you will probably be stuck using factory exhuast manifolds. A 428 with a 390 truck oil pan on it would clear fine, but exhuast would be tough.
The other thing is a finding a tranny to fit the app. Im pretty sure the only manual ever used behind a FE motor was a NP435. And it would probably take a special adapter to mate it to your Tcase.
Also, the FE motor is huge! and heavy.
What I would do is a 5.0L h.o. motor mildly built, making around 350-400HP, and still EFI.
Or, take a 351W, buy a $400 crank, and use stock 351 rods, and stock 302 pistons, to make a 393 stroker. port the heads a little, add a comp 4x4 extreme cam, and a good intake and carb. You will be looking at 500+ hp very easy, with huge torque down low.
Plus by useing a T-18 tranny, you can retain halfways normal parts.
89 SSV mustang, 4.10's, mac equal length, O/R H-pipe, pullies, short belt.
89 F-150 359W, 600 holley, headman, ported heads, T-18, Ford 9", spool, 5" lift, 35" bfg KM MT
84 broncoII 302, 600 holley, 484"cam, jacobs, ladder bars, fender exits.