Going to replace Edlebrock 650 with 500, what can I expect?

[truckster]

Summit has remanufactured Quadrajets for about $300. I would call them and talk about your specific application, and they can make sure you get one that's jetted and set up right out of the box.

[Longhorn 70]

Edelbrocks are SO much easier to work on than QJets. If you do your own work this may be something to consider.
1.You also do not have leaks in Edelbrock like the QJets.
2. Edelbrock has no gaskets below float level.
3. Floats are adjustable without taking the carb off the vehicle.
4. Needle and jet changes much easier for easier tuning.
5. Hold off springs also easily changed.
6. Pump stroke changes in 10 seconds.
7. More flexibility in tuning.

I think the 500 is enough or 650 if you are in high altitude.

BUT ALL THAT SAID. QJets were the original equipment. Still Edelbrock gets my vote.

My Big Block Olds, mildly cammed and HIGH compression with an Edelbrock 750 on it gets 15 M.P.G. if I drive mild.