Carb recommendations for my 340

On the street;
As for size, any 4bbl from 580 to 800 will be fine. the smaller ones are more responsive under 60mph, with street gears.
As for easy to work on, it's hard to beat a Holley.
As for the hiway, a small spreadbore is the way to go, and with metering rods is even better.
Over all, the Thermoquad is , IMO, incredibly versatile. Personally, I love how the TQ roars with an automatic, and unsilenced air cleaner. You can hear them working from a long way off. And from the front seat, it's magic.