F350 Transmission questions

I have a 92 2WD F350 with a 7.3L Diesel and an E40D transmission (which is the problem). My neighbor's kid has a wrecked F250 gas burner 4WD which the
father wants to get out of his yard. I haven't checked yet and the father knows very little about the truck. I did look inside the cab and the shifter is the same as on my truck (with the 'knob' on the end for the OD) and the dash is the same. I don't know the 250 has the E40D transmission (but I'm hoping) but if it does I need to know a few things before I talk with the kid about money.
First is there any reason why a E40D transmission from a 4WD would not work on a 2WD?
Second how difficult is it to R/R the transmission in these trucks
Third is there any real mechanical difference between a 250 and a 350? I would think the main differences would be in the suspension system and maybe in the rear end gearing.
Also can anyone give me a hint as to what would be a fair price for the transmission alone and for the entire truck. FYI, the truck hit a tree and took out the front end and bent the frame. The father thinks the motor is shot but isn't sure. So please make a guess about it running and another for if its not. I know a running engine would make the truck worth more but a gas burner is useless to me. The interior is in fair shape but the glass is busted out so it has been exposed to the elements for quite a while (6+ months).
Well thanks for any info you can give me.
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the back of the trans is different. the trans will not work without modification to the cases. diesel and gas transmissions are not the came cases, so they will not interchange. most automatic transmissions out of wrecked vehicles are not worth using, unless it has no mileage on it.

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