Several months ago I made a serious inquiry about this boat. I didn't want the gasser and given that the ad says that they will consider repowering with diesel, I spec'd out a Cummins 6BTA and a Northern Lights genset to replace the two gas engines. Never heard back from the seller and bought another boat.
So I assume they are only interested in selling as is with the gassers.
It would probably take 250-300 hp to move her at 15 kts which is doable with the 8.1 gasser but it would only last at best a thousand hours at that rate and burn 20-25 gph of gas.
David