I never have checked but I think are the same as the 14.5+ OHV singles.
Now as the engine running just be aware that v-twins can run perfectly good one cylinder until loaded so when you get the carburetor straighten out test that both cylinders are operating and fairly balanced power wise. Otherwords they the rpm drop when one is not working should be nearly the same as the other when swap the firing cylinder.
As for the hydro most fail due pump failure (center section). It usually very costly to repair and replacement is about the only cost effective option as you may be able to get a good used unit as a replacement for a reasonable cost.
As for being a Massey I haven't seen their setup so it might be repairable but check the costs first.
It also just might be a bad axle seal that leaked out all the hydraulic fluid.
