Thanks.
How substantial is the Dana housing where the cover bolts enter, and what size are they? (I'm sure some here will anticipate where I'm going with this).
If the housing thickness is sufficient as an "anchor" point, the cover could be stiffened a great deal by simply adding an "X" brace across the dome (landing in between several bolts). This should be as tall (standing away from the cover) as practical. It serves as the attachment point for 2 spans (1" 4130 tube) each ending on a big adjustable clevis on either end (like a 4-link). The cover's new addition and the housing axle ends have the mating clevis shapes.
When assembled, the spans pull the axle tubes backward toward the landing spot on the cover to whatever tension you want on the clevises. The taller the X brace the more leverage the clevises have.
To service the gears, back off on both clevises a few turns, and remove the pins holding the inner spans to the cover; rotate them down and out of your way (or remove completely if they're in the way).
The cover now comes off as normally.
Service complete: attach the cover, tighten the clevises and re-install the pins through the spans.