Got my trans back, it will be awhile before I get it installed, but I think I'm ok.
The 2 main things I have going for me is this 518 yoke is 1.0 - 1.5" longer than most 727 yokes, and there's 1.25" of splined shaft beyond the case end.
The numbers in RED are if the yoke is pulled out an addition 0.5", looks like I still have 3.25" overlap on the splines.

Check my math, hopefully I'm looking at this correctly