Hello SVO42:
I have a 81 Mustang with a 1970 250 motor in it.
My father bought it brand new in 81 (I was only 15 years old at the time)
the Mustang came with the 200 motor from factory.
When I started college my father gave me the car to drive back & forth to school.
We had a 1970 Maverick Grabber at home with the frame rotted out of it so I took the 250 motor it had and had it rebuilt with some performance goodies (Isky cam, Rhoads lifters, head work, Clifford header, ect...)
Anyway, what I thought was gonna be an easy swap wasn't.
Yes the others in this forum were right, there is no rear sump pan for a 250 motor.
I made one by using the top portion of a 250 pan and the sump portion of a 200 pan and migged the two together.
Also you cannot use the 200 motor mounts. If you do the motor will sit too hight in the engine compartment and you will need to cut a hole in the hood and add a scoop. Which you still have to do anyway as the 250 motor is 2 inches taller in the deck height than a 200.
You say you would put this in a 87 Mustang?
87's did not come with a straight 6 motor in that year. You must either have a V6 or 4 cyl. I think you will have to switch K-members with a earlier car that came with a 200 motor. All fox bodied cars had the same engine compartments so the K-members will switch.
I still have my 81 and the next plan of action is a T-5 conversion and a Holley 500 cfm 2 bbl. switch.
If you need any more info - just ask!
John