I'm just guessing that your 28mm would have the same setback as my 28-90
I don't see any basis for this assumption. The lenses are a completely different designs.
As a rule of thumb, lenses that fit the Leicaflex SL are likely to clear the mirrors full-frame CaNikon cameras. The 28mm Elmarit-R is OK on the Leicaflex SL, the 28-90 zoom isn't.
I measured both my 21-35 (shaved to fit)and my 28-90 (not shaved) vario elmart from the rear most portion of the flange and the rear element (leitax mount installed) and you need 5/32" or less to prevent mirror interference.
The mirror swings in an arc so the diameter of the rear protrusion matters too.
If the zoom works OK on Marc's D800E I see no reason the 28 wouldn't because it has more clearance than the zoom.