The USD double tank manifold on steel tanks of the time were no problem for a double hose regulator.
There is a problem with some combinations with the USD twin manifold and the AL tanks, because of the difference in the taper to the neck of the tank; those differences did not affect USD double hose regulators of the time (DA Aquamaster, Royal Aquamaster and Mistral). It does affect the Sportsways Hydro-Twin and Duel-Air (which have gauge outlets that can be a problem and force the regulator to be turned a bit). It also affects the AMF Voit Trieste II with a four-LP converter, as there is no room for one horizontal hose coming off it. There is no problem at all with the Nemrod Snark III, Healthways Scuba (all versions) or older Voit double hose regulators (which are the same dimensions as the USD double hose regulators). All these problems with AL tanks and the USD twin manifold can be readily overcome by simply turning the center section over, so that the regulator attachment is above the manifold and the on-off valve is between the cylinders. But by doing this, it is not possible to turn the tanks off while they remain on the diver's back.
SeaRat