Greetings . . .
My only concern with using exhaust heat into a jacket designed for water would be getting certain spots on the manifold 'over done'. I have an Edmunds 2 deuce that is designed for water heat:
I would think that exhaust gas would over-heat the entry-point sides of the manifold, which would transfer up into the base of the carb. An insulating spacer might compensate.
Water heat is indeed slower - but its uniform.
regards,
Keith