I have dry stainless marine 4in long tubes on Pantera 28 with twin BBC , hasanyone had drew shot guns on dry pipes ? do they work? willthey fit?

they should work ok, as long as water exit is at end of pipe. if you have isolated water dumps, probably not good idea because of overheat possibilities.

Water dumps are about the size of 1in diameter hole at the end of tube on under side. do these need air pump ?

i believe the drew shotguns are self actuating, and do not require any other hardware. however if your pipe dumps are on the underside of the pipe, i dont think they will cool the silencer. the water would have to mix with the exhaust at the tip of the pipe. your pipes could be modified to work that way, by simply drilling a 1/4 hole in the inner pipe at the end of tail pipe.