Ok, well, I bit the bullet and chopped into this thing. Rather than settle for hanging a DIN 1st stage off the surface supply port of the unit, I chucked caution to the wind and cut into the ADV supply pipe inside the clamshell and spliced in a small brass 4-port manifold with 2 of the ports tapped to 3/8 UNF...
Thus I have been able to fit a bail-out reg and inflation hose into it. These hoses run out through the cylinder valve access holes and up behind my OMS wing.
I've also replaced the soviet SPG bulkhead fitting with a 7/16 UNF setup and attached my Oceanic air/nitrox integrated computer.
More photos in the Homebuild gallery... search on Orca.
Ray.