The last time I had a Holley on a stock compression, stock head motor, it was a 600 cfm vacuum secondary with electric choke. I was never dis-satisfied with that combination, as I don't think the secondaries ever opened up! The 500 should work fine also.
The only recommendation that I can give you is to make sure and get the tailpipe emissions checked as soon as you can. If the carbon monoxide (CO) is higher than about 4% to 6%, then seriously consider rejetting the carb. Usually you would want between 2% and 4%. If it's higher than about 8%, then the motor will wear out prematurely due to a phenomenon called "cylinder wash-down". The too-rich mixture causes the engine oil to dilute and then it cannot protect the walls and rings properly. The higher the CO, the faster it wears.
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David
newbie #4153
