the Sherwoods don't have full parts availability *valve seats*, but I think that's it. Dive Rite, OMS, and Thermo all made them and with the exception of the neck o-ring which is an off-the-shelf part, there is no difference between the standard 3/4 and 7/8 manifolds. If you have a good machine shop you can always have a 3/4" valve turned down.
I know this is an old thread but has anyone actually turned the threads down? if so what are you doing about the chrome plating? After machining and re-plating wouldn't it just be cheaper to buy a new set?
I can cut threads, and I sure could use another 7/8's manifold...