Doc, a lot of Marlin and NEF shooters would love to have your problem. Those barrels tend to run loose. Your bullets should size to .459 easily enough. Bullets often run heavier than nominal with WW. My guess is that the nominal weight is for linotype.
You should be able to get your as-cast diameter down a thou or two by using half WW/half lead and running your alloy and mould a bit hotter. The added lead reduced the proportion of antimony, and the hotter alloy has a bit more shrinkage when it cools.
The extra weight won't matter a bit as long as you stay a grain or two under max loads. You'll probably want to do that anyway for reasons of recoil and accuracy.
More details on what you are shooting and what you want to do would let us help you more. There are a lot of variables in cast bullet shooting and more for the .45-70 than most calibers.