The choice of bullet will dictate the cartridge OAL, with regards to its nose shape and range of diameter along its effective bore length. Early on in my career with the .45-70 I trialed the Lee 90577 and found it not consistently accurate for 200 yards let alone longer. I'm an advocate of light compression with Swiss powder and never loaded a .45-70 Starline case with less than 65 grains of 1-1/2F with no more than .060" compression under a variety of wads such a .025" milk carton to .060" LDPE. In your case with that Lee bullet it sounds like something is amiss - perhaps it's casting oversize, or you didn't size it, or the bore is less than .450" for at least where the freebore ends which should also take into account the freebore length past the chamber mouth.
Yes, the Lee bullet molds are cheap, but they are in no way as good (as in "consistent accuracy and performance") as more expensive molds from makers such as Accurate, Lyman, BACO, and many others. It really does the rifle no good to use an inferior bullet design and mold, for as with archery, where the arrow is far more important than the bow, so is the bullet to the rifle. But, lots depends on what will be the primary use of the rifle.