Hi Dave. Sounds like you’re hoping for a SD owner with drain tubes to come along with some photo’s and measurements. There was one at Grafham water centre when we did our RYA level 3, don’t know if they still have it (it was about 15 years ago 😯 ). They must have had a standard-sized tube because they used expanding drainage plugs to block them which seem to come in 100 and 150mm diameters.
Give Ian Porter a call. He will should be able to explain how they built their SD’s, and he’s probably seen a few Moores boats in his time too.