kadee couplers for athearn rtr sd50

i want to order a pair of athearn sd50’s and i dont know what size of kadee coupler to order![:(] the ready to runs have the snowplow so i need a longer size can anyone help me?

Rewiew the merits of the #26, extra long shank

http://www.kadee.com/htmbord/page71.htm

I have a RTR SD-50 if this is what you are referring too. It comes with knuckle couplers installed. I believe they are the Bachmann EZ mates. This is the style that has a spring as opposed to the standard Bachmann coupler that has the plastic spring bar. If you decide to change them anyways, I would wait till the come in and use the installed ones as a length guide for the KD’s.