71duster, do they actually ahve T-quads available? I took a quick look and besides being a mainly GM carb biz, they offer an "aluminum Quadrajet to replace that problem Thermoquad."
Not sure what you are referring to, because that site is all mopar and all thermoquads.
I had them rebuild a TQ for me after I gave him my engine build specs. Before that, I had a brand new Holley 670 Street Avenger on my 360, and I HATED it. It idled like crap and I could never get it tuned up right. I bolted the TQ up right out of the box and haven't had to play with it since. Definite performance increase over the Holley, and purrs like a kitten at idle. I would recommed Thermoquads.com 100% - he actually posts here under the name Demonsizzler. He knows everything about TQs - you should pick his brain.
As far as your intake choice - The Performer RPM and Air Gap only mount squarebore carbs, so you'd need an adapter or a different intake. My 360 was originally in my truck with a stock iron spreadbore intake, but I'm now going to use a Edelbrock LD340 modified for a spreadbore - so no need for adapters, and from what I've read, should perform pretty darn close to the RPM manifolds.