Don't know anything about the Ford 4.0, but the 05 and later 4.7 is extremely reliable. The earlier ones had a habit of spitting out the random cam follower and having a cylinder go dead- no damage done, and there are many youtube videos showing how to pop the follower back in with a screwdriver. The later engines (after around 2003/2004) don't do it anyway- it was a matter of reducing the total travel for the hydraulic lash adjusters. Among those youtube videos are some showing how to just shim the HLA's on older engines so the follower can't pop out on them, either. The 4.7 block is built like a battleship- its a small-displacement engine but the 5 main bearings are all carried in a single "ladder" casting that bolts to the bottom of the block between the block and oil pan, pretty much creating an assembly as strong and maybe stronger than a deep-skirt block with cross-bolted main caps. You're NOT going to scatter a 4.7 from bearing movement or crank distortion... period.
The 08 and up 4.7 is actually even better with a revised cylinder head, dual spark plugs, and 310 horsepower instead of ~240 for the 07 and down non-HO versions. But the Hemi overshadowed it, and once the 5.7 Hemi got MDS it also delivered better fuel economy, so the 4.7 was effectively replaced by the Pentastar v6.
4.7 "sludge" is a myth perpetuated by the fact that the first application in ~98/99 had a tall oil filler neck that would form a white condensate emulsion right under the oil cap because moisture would get up there and there was no air flow through the filler neck to clear it out. Engines with a short fill neck don't don't do that, and NONE of them sludge any more than any other engine (in other words- sure, if they're severely neglected).
