I don't fancy myself as an expert on the subject, especially since I've had my truck in the Project Purgatory wing of my shed for way too long. Anyhow, here's some photo's I shot before I pulled the 4200 out to do an IFS crossmember install on the 54. I would have more, but some photo hosting sight has taken my pictures prisoner.
Anyhow, the 4200 is slightly longer than a 216 or 235, with that being said, from the bellhousing to the Dampener, It's actually about 1/2" shorter than the 235 is from the bellhousing to the radiator fan. The engine is an 08/09 model with an AR5 manual transmission bolted to it. Earlier models actually have the exhaust manifold tucked in a little closer to the block, so no real clearance issues there. I've since decided not to go with the AR5 and in fact, I picked up a 2wd 4L60E this past Saturday. Size wise, the 4L60E is actually slightly smaller than the AR5. The motor mounts I'm using are a combination of 3/8 and 1/4 plate that I made on the engine side and Competition engineering mounts with Ford Taurus solid rubber isolators. I trimmed the engine mount portion off of the lower radiator support for a little extra clearance. It probably wasn't necessary, but it helped when I wedged it it there. since I don't have the engine/trans. crossmember removed off of the 54.
With all that said... The 4200 fits quite well. Ideally, I would like to slide the engine back slightly further. That would require some sheet metal clearance for the Intake manifold and that's about it. The bellhousing is actually smaller than what the V8 trucks have, so there may need to be some trimming for it, but I doubt it. I'm actually still thinking about leaving the factory 54 engine crossmember in.