Get rid of thoes stock carbs first off, I'd say go with some 34's. Im just wondering,, how much compression do you have? If you really wanna get some power out of that motor put a 4mill crank in it and use a spacers plate since your at a 66 bore so you can still use your 513 series pistons you will be able to get 1 more bore out them if anything were to happen and that will be a 66.5 thats the most you can go on thoes cyl's. ohh yeah you can have your flywheel lightened also.