Would the 4.7 liter from my 1999 Jeep Grand Cherokee fit in an A body?
A 5.2 Magnum wouldda kicked its ***.
The 4.7s are alright. Fuel mileage? It'd actually probably be decent in a car, provided you didn't mind having to adapt heavily for the oil pan. Of course, a Magnum would probably be very close to it.
Its real problem is that they took a page from the beginning of Ford's notebook and burned the rest. They redesigned the motor, kept a select handful of things the same, most of the vehicles were re-optioned to compensate (Jeeps enjoyed this, many Daks/Rangos were SOL in that department), but Chrysler never really progressed the design. For the little things they are the 4.6s and 5.4s along with their successors are very good in cars and light trucks. (though the V10 is awful compared to Dodge's)
The old transmissions will hook up to a 4.7 the same as a Hemi- the flexplate's different. (I think that's it- besides the asymmetric/symmetric issue Magnum/pre-Mag transmissions)
I think the limit to what would you swap a 4.7 in goes down to- is it cheap, is it better than what I've got by a longshot, and will I have to change the oil pan? For an old truck, it qualifies- but for a car, no.