The 32-40 Winchester case tapers from 0.424 to 0.3455 and then has a neck of 0.3388 (OD) with no appreciable shoulder. The ID of the neck is slightly under 0.321. That gives you a wall thickness of about 9thou.
If you were to open the neck by 0.002 to 0.003, I would say you woild have no problem at all with the 8MM bullets loading in the dies. Brass thinning would be negligible, in my opinion. You will have to have the seat/crimp dies relieved for the fatter neck, even if you use an 8MM expansion plug in the sizer. I would also relieve the neck portion of the sizing die, to reduce the metal working of the cases.
I don't know about the rules for competition in any of the replica/antique groups, but those questions should be easily answered by the organization. Just ask about using an 8MM barrel on a 32-40, as if you were rebuilding.
Lee will build dies to spec for a fairly reasonable cost. You might try talking to them and seeing what they recommend. All you are asking for is a mold for the 32-40, with a (more) spitzer nose.
Those are my thoughts and probably worth about what you paid for them