Engine leaning out at 3000rpm

Well to start with if you have almost 500 cubic inches, i will say start with an 850 cfm carb and get it tuned. Unless this is a trans brake race car you need a power valve in the primary side. I would say start with 76 jet in front with a PV and an 88 jet in the secondary side. Go out make some top end passes stop pull a plug. Jet up or down till the plugs look a nice tan brown and clean. Then squirter time. From a dead stop swap feet floor it see what car does. Keep going up in squirter size till it blows black out the back, then go down 2 sizes. Or go to the track jet for MPH and squirter size for 60 foot. This is a tried and true method. This is why i spend the extra $600 to engine dyno, then there is no guessing and you always have a base line to go back too.