Finally got the backplane ports section of the 9500 donor case (shattered plasticitus syndrome) fit snugly into the slot I cut into the Netra's armor plate in the update above.
Took a bit of doing. Shim on 1x4 scrap and liberal application of hot glue to jig and panel squared up the slightly off top edge. Then I was able to use that edge to rip the bottom edge to square up/correct fit for slot. Cutting would have been easier on the bandsaw, but I think I got a cleaner edge with the wet tile saw, crappy rip fence notwithstanding.
Mark I eyeball measurements of fitment are lookin' very good. Height is right on for audio jacks, but I'll need to shim the other side's and center standoffs to bring the SCSI port into alignment. Once all is hunky dory for the 4U 6500 effort I get to play the same games putting new standoffs for the PEx board.
Technical observations:
Loving the lack of onboard video on the 9500 with that knockout to cover the port for it. Makes it just perfect for this Batch A EVTA PEx/PowerMac6700 ProtoBoard which lacks the onboard video subsystem.

Wondering if they'd intended to use that godforsaken crumblecase for the 9600 given that knockout.
Gotta fab a "knockout" for the AAIU port opening though. They dropped AAUI from 9500/9600 and going straight up 10bT
only at long last!
Idiots at the Infinite Loopiness should have dropped the long obsolete DA-15 video connector and gone straight up HD-15 VGA, but noooooo!
PEx
FINALLY moved from Fast/Narrow secondary internal only SCSI bus to UltraSCSI, both inside and out! Connector's different and may need a tad more clearance for the cable retaining "earclip" on that side next to the AAUI hole. Looking forward to seeing what a pair of my 2.5" Savio UltraSCSI server drives will sound like through the filter behind the grated drop-door front of the case.
Don't recall ever reading about that SCSI upgrade anywhere online, just noticed it. Beige G3 moved to Fast/Wide SCSI via PCI Card, so UltraSCSI would be dependent upon card installed?
Two ATA Bus connectors is a nice touch.
edit: I'll try to get a higher resolution/clearer pic of the board to swap into this post.