Thickstun dual intakes were produced by Tommy Thickstun in California around 1940. They are good hi-rise intakes and bring a super price on ebay. In the last couple of years I've seen them go for $250 - 300.
The hi-rise keeps the carbs cool and helps break up fuel droplets. Horsepower would increase just because you have 2 carbs at work. Another advantage is you can run a stock generator setup with them since they're not the 'super' manifold type.
The car/truck version was model PM7 and I understand there was a PM9 that was made for boats with slanted carb bases.
FWIW, I read last week on another site, Ford Barn, I believe, where there reproducing the Thickstun high rise manifold. If you're looking for one you may want to check this out. I believe there was a phone number in the post. Good luck, Carl