340 carb size

Hi guys,
I am thinking of changing my carb on my 340 duster .Its got a 750 vac sec holley and iI think its too big.when I had the car on the dyno it was down on power.we found a cylinder low on compression.some one ground the rockers to get valve clearance and one rocker pulled the valve wore the valve guide and buggered the valve seat so of with the heads fixed the seat and guide.I looked at the ports and got the dye grinder out and cleaned mhem up.I tryed to find some ajustable rockers but no luck(mopar parts are hard to find in NZ os I ordered some roller rockers to fix that drama and thought I should look at the cam,it was abit small so new cam kit and push rods was ordered from the states.the cam is a .497 lift with 1.6 rockers.the old cam was .420 lift .I thought this will wake it up but not as good as I thought it should.The car is a 73 340 duster with headers full MSD alloy high rise duel plane inlet manifold,shift kitted 727 and 3.91 suregrip rear.What size carb should I be running?