I bought a set of near mint condition twin 30's for the pair of 30's to use as deco bottles.
Consequently I still have the like new USD twin manifold and the spacer designed to go between the two tanks.
30's and 40's are the same diameter so it would work equally well for twin 40's. THe way the mainfold and spacer are designed, the set wil strap to a regular BC or a hardpack with a normal cam band. I did have to dive the arrangement before dissassmbling just to see how it felt and they are both light and low profile and were well balanced.
If you are interested we could possibly work out a deal.
A set of triple 30's would be cool just to have and use them with one of my double hose regs.