So after a few beers and about an hour of measuring yesterday I came up with a plan to fit two modern Sterns in my 07' Yukon XL.
The problem is that you can't turn them sideways because they're too long by about an inch (even if I removed the shooter rod housings).
So with the third row seats removed and middle seats folded up against the front seats, I was able to stagger the pins backwards to each other and "stack" the backboxes giving me enough room to tuck them in nice and snug next to each other.
I am a very happy camper right now
P.S. Big shout out to BellBrande for being awesome and her support cheering us on as we ventured into the ancient unknown art of "pin stacking"