Mike:
I like your car, the photos look good.
I think you're right on the money with your idea to put a water jacket to heat the carb plenum. I have read other threads in the Bulletin Board that go into great detail on the subject. These threads are on naturally aspirated manifolds, but i think the principle would be the same, especially if you have condensate on the outside. I didn't look back, but i bet if you do a search on heated intake manifold it won't be hard to find.
What material is it made of? It appears to be steel. I have a similar setup, but with an Eaton M90 supercharger & Edelbrock 600, and my carb plenum (aluminum) drops about 1/2" below the blower inlet. (for the same reason you stated, to keep the carb low) Mine performs well, with no flat spots (after about 5 minutes of warm-up), so maybe the aluminum conducts a little more heat out there than steel would.(?)
But i have considered heating it for cold weather driving.
Anyhow, i hope this "rambling" will help you sort out your Rambler. lol
Good luck!
pappy
p.s: pages 7 & 8 of the link below show my setup