I'd spend the $35 extra and get a brand new one.

My mechanic wants me to get rid of my Holley 750 and put in an Edelbrock, he is a vette specialst and thinks they are the best going right now, although he hasn't worked on a Speed Demon for comparison, but he just hates Holley's.

Just to update everyone...

I opted for a shiny Holley 650 with an electric choke. Out of the box, onto the car, no A/F tuning needed, just had to adjust the choke, and voila! Beautifully running car... Seems like it's a good size for my punched out 350.

Imran - 74 Convt

Glad to hear that you are happy with your Holley, I still tink that I maybe overcarbed with my Holley 750 dp. I am running a 383 stroker with an original Torquer intake, slighlty modded, Dart heads. Lots of top end go but low end from 1500 rpm - about 3800 is not that great.

Red, There are a few possible reasons why your bottom end is not performing well.
First, I think you are right about the carb being too much. At maximum volumetric efficiency (which can only be acheived with an all out racing engine) a small block chevy can only take in about 650 cfm max. Most street small blocks can only realisticly take about 550 cfm.
If you like the double pumpers, I would recommend a 650 DP.
But for better street performance, I recommend a 600 vacum secondary.
Second, Is your intake a dual plane or single plane?
Most single plane intakes are designed to deliver power above 3000 rpm and are mainly for racing. A good dual plane will give you great street driveability and good top end performance if you want to do a little racing. I personally like the Edelbrock "performerRPM" manifolds. It gives me good driveability and very good top end.
Third, what cam do you have in it? If you have a high lift with a large overlap and a lopey idle, you will not get much vacum until you are at higher rpms. The carb will need to be jetted and the correct power valve installed to match your cam.
I suggest giving the tech guys a call at Jeg's or Summit and give them your cam specs and drivetrain info. They should be able to give you a recomendation for intake and carb combo.
Hope this helps, Mark