flat top are dished

Can't help you on which kit to get. But, if you're sure you're not going to huff or spray the motor, I'd go with the flat-tops. Dished pistons will increase your combustion chamber volume, which lowers compression ratio - and that generally lowers the amount of potency/efficient use of each of those 2000 explosions per minute (at 4000 RPM). More pressure when it goes bang = more torque (at any RPM) on the crank/clutch/tranny/driveshaft/axle/tires. To paraphrase somebody else's signature line: "Build for torque! Horsepower is something you brag about in the parking lot!"

first stay far far away from the high volume oil pump. you dont need it, and it will tear up your distributor gear fairly quickly.

as for piston tops, i prefer either the flattop or a reverse dome piston. a reverse dome is a dished piston where the dish is contoured similar to the combustion chamber shape, and not just a trough cut in the top of the piston. use a reverse dome piston with a small combustion chamber to limit detonation, and keep the compression ratio reasonable. if you have 64cc or larger chamber, then use the flattop pistons.

you need a high volume pump when you have large bearing clearances, and are running thin oil at high rpms. that way you have enough oil volume at the higher rpms to feed the bearings.