OK, here's the deal...I got 2 Bachmann starter sets (I know, I know...) for a steal on Ebay, brand new. I'd like to convert the couplers on the sets, but I'm not sure what I need. I've got the Empire Builder set, which has a Northern 4-8-4 Loco and Tender. I've also got the Thunder Valley set, which has an EMD GP40 Loco. Can anyone help suggest a mag coupler to convert these to? Thanks!