From parts in my junk drawer... I had a F3 burn field and a good field to use . I looked at the rivets holding and messured AND the F3 motor and Alco 200 series ARE the same
IF you look my field was bad so I put a new Used one in..
IF the field was good all you do is drill and tap with a 4/40 tap
Then grind off the nub on the bottom of the f3 motor so the gear when assembled wont hit
The Alco top with the field just drill out the rivets by hand..
This will be a direct fit! JUST screw in the 2 4/40 screws to the top plate!
The Lionel engineering department might of went cheap BUT someone thought ahead . someone must of known a f3 could fit in their!
Anyways put it back together and have a UNBELIVEABLE pulling smooth and quiet running ALCO 200series rev-1.lol