If I remember correctly, there is really only two length Model 70 actions, long, and short (and maybe one for the WSSM family of cartridges). The magnum Model 70 I believe just used different magazine boxes and different length ejectors / bolt stops for the 375 H&H family of cartridges vs the...
In my experience N340 meters fine. I wouldn't be worried about throwing 4.2 gr charges of it. I would get the small metering assembly from RCBS as it's designed for throwing smaller charges that are more suited for pistol ammunition...
If you don't already have a balance type scale you should get one just for the fact that electronics don't last forever, and the mechanical scale will. I have a couple of electronic scales, but wouldn't ever be without a mechanical balance.
With regards to loading 9mm ammo. I'm assuming that...