Holly carb advice please

[dave`12]

1967 c-10. Factory sm430 and 12 bolt rear. Fleetside.

I put in a 350 (mid-eighties, I think) with an edelbrock performer manifold, ramhorn exhaust manifolds, dual exhaust. I got the engine off craigslist, so I really don’t know more.

Right now I have a very tired holly 650cfm (came free with the engine). Tried to rebuild it, but didn’t help much. Truck runs very strong, but I’ve had some issues with hot start after sitting, poor mpg (around 9mpg), and it only runs strong when it’s so rich that the fumes make me sick.

I’m tired of messing with it and so I’ve decided to get a new carburetor. I’ve been looking and found a couple of options, and I would like opinions if I could.

Holly street warrior. I can get this remanufactured (by holly) 600cfm for 220.00 on ebay or 320.00 new at holly. Here is a link to the new one:
https://www.holley.com/products/fuel...parts/0-80457S

Holly classic: https://www.holley.com/products/fuel...parts/0-1850SA This is 315.00 new at holly.

Holly street demon. This one is quite intriguing. I can get it for 220.00 on ebay remanufactured by holly, or 312.00 new from holly with a composite fuel bowl that is supposed to lower fuel bowl temps by 20 degrees.
https://www.holley.com/products/fuel...mon/parts/1900

Does anyone know about the street demon? How about the composite fuel bowl. It would be about 100.00 extra. Worth it? I’ve seen some reviews on the carb. I have a square bore manifold, and this is spread bore, but designed to work with a square bore – so I’m thinking it would help my mileage. One guy got an extra 3mpg when he swapped.

How about fitment? Problems with my current air cleaner and linkage may exist?

Other new carbs would be considered (edelbrock etc.) But I want an easy setup and I want to keep the price below 350.00. The street demon link has a video, and the guy sandwiched a metal plate with two paper gaskets when doing the install. Is this to help with heat transfer? Maybe I should get a small spacer for heat transfer?

Any opinions appreciated.

thanx