Looks like a nice piece of work.
It's really a tossup
With the stub shaft, you get more oil flow to the rest of the engine. With the turned down shaft, you get better stability. But keep in mind that this is the *driven* gear. The gear with less support and more load (once the balance weight is gone) is the drive gear, which is loaded by the timing belt. The turned down shaft will put more inertial loads on the drive gear, since you have to spin up the shaft. Both have advantages and disadvantages.
Either option will work better than the weighted shaft. If you're going to stick with the original pump and gears, cutting down the original shaft is probably a better idea than just sticking a stub shaft in an old pump.
I think the most important thing is to use a brand new oil pump with brand new deburred gears. The most likely cause of failure is going to be using either used gears or a used pump housing with wear patterns that don't match eachother. Also, stick with the straight cut gears over the helical ones. The latter will be quieter, but will create side loads on the casing. (Helical gears can take higher loads, but you're unlikely to actually break an oil pump gear)