Hi Scott & welcome to the forum.
A quick forum search found only one Cougar 310SRX owner/member here, and unfortunately he/she hasn't posted
since joining a few years ago. That model was only built from 2007-2009, so there won't be as many to compare
notes... BUT... don't despair
Keystone typically uses a Lippert pin box, and chances are it's a fairly common model also used on that SRX.
If the current out-of-state owner could provide you with the pin box model #, then it's possible some of
our members (including those who own other SRX models) can offer some help with the measurements you need.
Good luck & happy trails,
Terri, the Chevy co-pilot