I have used 2 Aviator engines in MMs so far with great results so I'll speak from my experience. I look for the 2005 up becuase they have the re-cast heads with better cooling. They can be easily identified becuase Ford painted the left head with a big blue stripe on the outside above the exhaust ports and on the back side. This was per a TSB for head issues. It was a way to verify the casting number was the later head design.
You can only use the long block assembly. That is, the block and heads. Everything else has to come off the MM and go on the Aviator engine. If you want a list, here goes.
Intake, cam covers, flywheel, Front vibration damper, engine/trans seperator plate, oil dipstick, oil pan, oil pump pick up tube, windage tray (Aviator does not have one), front cover, coolant crossover tube, all heater hose tubes, the coolant tube down the center of the block valley. Also have to remove a temperature sensor from the back side of one head, and then use your old bolt that holds the battery cables to the rear of the right head. So everything except the block and head assembly.
While your in there, replace the oil pump (the MM one is the same as the 5.4 one, different part number than an Aviator), chain guides and get the metal lower tensioners (Ford will give you the plastic ones as a service part) the metal are the Cloyes units (who supplied them to Ford) and also used on the Cobra engines. The plastic tensioners use a silicone seal to the block that can blow out in under 10K miles. The metal ones seal via machined surface and can't blow out. Also they have a ratchet system to always keep tension on the chain.
Its not that hard. I would be a little suspect of a shop that could not figure this out. I did and I do it in my garage. We have had 6 MMs, still have 4. Good luck.
