This should be a simple one for you guys - how difficult is it to mount a Proto 2000 GP18 shell on a Proto 2000 GP20 mechanism? Is it (hope, hope) the same for mounting a GP20 shell and just a pop it on deal? Enquiring minds (or at least one of them) want to know...
Its been a long time since I swapped sheels on P2K locos.
The weights of the GP20 might interfere with the sheel of the GP18. The old brown/gold box GP18 and moving louvers in the grill which required space carved out of the weights for clearance. LL did not have those notches when they ran the GP20, IIRC, so I dont think it is an easy slip over.
If you have a big bluish box with red lettering GP18, LL changed the grills so they might clear the weights of the GP20.
Its hard to say without simply trying it.
- Douglas