Ranch Dog's bullet design is both tumble lube and gas checked. It should be a dandy choice. You won't have to size it except for the gas check itself. Definitely do not take a tumble lube design under .310. The small grooves are intended to be self-sizing in the bore and they already are gauged for crushing. I would, in your shoes, use a .310 sizing die in a conventional lubricator and sizer with these bullets, pushing the bullet base down in only far enough to seat and size the gas check. If you have only a straight-through sizing die, like the Lee, then you may find you want the bullets a little harder since you are going to be slightly pre-crushing the tumble lube grooves. The arsenic in wheel weights will let you harden them by quenching them in water. You can try just dropping them into water straight from the mold. That takes very regular timing, though, to provide uniform results. Frankly, I find an oven soak and quench more effective.
The Micro-groove barrel is both praised and cursed by cast bullet shooters. I expect a lot of it boils down to what velocities they are trying to achieve? One trick I used experimentally long ago was to set a little loop of 63-37 fine (.055") flux core soldering wire in the bottom of the gas checks, then heat treated the bullets in an oven sitting in the gas checks. That solder alloy is a eutectic for lead and tin and has the lowest melting point the combination can provide, so it melted well below the bullet alloy melting point. This soldered the gas checks to the bullets. Back then, Lyman gas checks were still straight and not the crimp-on type. My purpose was to keep them on the bullet in flight, and not separating and veering off into the chronograph sky screens. It had occurred to me, though, that the same technique might allow the gas check to apply some rotational torque to the bullet if the rifling was shallow, as with the Microgrooves. That's why I mention the idea here. AFAIK, all the 336's in .30-30 have Microgroove barrels. Not sure about the .308MX?