Aerostar 4.0 (4wd) engine replace with 3.0 (from 2wd) ?

Unless you are a jack-of-all-trades who can cobble together anything that he/she gets their hands on, don't do it. I think you will be better off in the long run to either rebuild the engine that you got or buy a rebuilt motor. OR, simply buy another van that is rusted out (how much rust does your Aero have?) and swap motors with the same size that you got. 40 years ago, that would be a simple job, but anymore you will be swamped with the problems you have swapping the electrical harness. Thanks to the rust factor, most Aerostar vans will rust out before they wear out, with the exception of an overheated 4.0 motor. Simply buy a rusted out van with the motor you want and either drive it or swap motors.

This advice coming from owning 4 Aerostars and having over a million combined miles. YMMV.

That's what I've thought as well, mainly because the electrical system is pretty much different in 3.0 and 4.0. And all accessories different and in different locations so might need to swap almost everything.

But I saw that somebody has probably done it, see

It's in Swedish but heresome translation: "Motorn =E4r bytt fr=E5n en 4.0 till en 3.0:a." means that engine has been changed from 4.0 to 3.0. But that's the only part of the ad mentioning engine, all other text in ad is about different parts that have been replaced et.c.

Might be easier to just replace all lifters but that's almost a cost of whole 3.0 parts van.

The 3.0L is a better engine, and a manual transmission would be a better choice again.

I would hire either a local ford repair mechanic to do the job on the side or hire a good ford (dearborn) employee who knows what to do. Engine, computer, wiring harness...... this is getting expensive.

Good luck, Dave