Kindly keep your pants on!
Your request isn't exactly mainstream where knowledge based 'off top of head' responses work! Typically, I don't begin to write-off a 'no response' to Thread or Post for at least several days! So! That said...
Photos of a couple of 338 WM Supergrades. First pre & '64 & then 1992-93 WRAC model. Note that the swivel connector-width differ. I suspect most measurements between these genre rifles differ in most respects. The 'pre' model is simply more robust. The advisory that I'm working here from my photo files and without reasonable opportunity for measurement. I've tried to represent fore & aft swivel locations as possible considering my pix weren't originally contemplated for publication of any sort.
Hope this helps!
Upper several pix of the pre '64, lower two of early nineties era Model.
Best & Stay Safe!
John
