detonation / knock issue on 340

I do not mean this insulting in any way shape form or fashion, so please take it in the intent it is given. If you do not have good and I mean GOOD carburetor tuning skills, don't get a thermoquad. They are great carburetors, but the learning curve is pretty steep if they are new to you. Also, if you run a square bore carburetor on that intake, you will need the thin plate from Edelbrock to assure you have no vacuum leak around the secondaries. This is all you need. Most O'Reilly stores stock it.

Edelbrock 2732 Edelbrock Carburetor Adapters | Summit Racing