Well my sons 85 re 4x4 is on its last leg 290k mi. And a 90 re motor with 70k just popped up for sale. The motors from a 1990 2 wheel drive. Is this going to be a prob.? Sons 85 is a five sp. Don't know what the 2wd had. Brad

 

id give the dealership a call

 

If the production date of the 85 is late enough then it will have the right engine compatible with the 90. 2wd 4wd doesn't matter. The only thing that might be different is the Oil pan???? If so, then the oil pan from the 4wd would have to be swapped over.

If it's an earlier 85 it might have the short deck motor. I can't speak for the engine mounts but I believe they are the same between the 2 different engines. If so then the 90 engine would bolt right in assuming the oil pans are compatible.

As far as the difference in sensors in relation to tall and short block 22re's I am not sure on that.

With that being said,as long as the short deck sensors are compatible with tall deck engine, easiest way would be to transfer all of the engine sensors over to the newish motor. Fuel injectors, AFM, etc etc. This way you won't have to use the 90's wiring harness, ECU etc etc.

 

So how would I tell if it was tall or short deck? I can look at the build date of the 85 (trucks not here now). The 85 it self is loaded with every option. I've only seen 86 up like that. So it might be later build.
Let's assume the 90 motor truly has 70k would it be wise to bottom end rebuild or try and squeeze another 100k and not rebuild.

 

so that depends on budget it is always a good idea if you have the money to do the bearings why you have it out and check the rest of the engine and replace the front and rear main seal when you swap the pan also the small things like the thermostat and timeing cover gasket just in case but you could put it in and hope for the best and possibly get away with it

 

it should work like xxxtreme22r said the oil pan might be different

 

Swap in the 4wd oil pan and use the intake, injectors and sensors off your 85 motor. Since you have it all out, it wouldn't hurt to have your injectors sent off to be cleaned while your putting it all in. Remember, you need to use the electronics off of your 85..that way you can use your wire harness and ECU that's already in the truck.