My experience suggests that you should be able to get away with the cone being-more-or-less the same size- I've not had any fatal problems with mixing and matching- fractionally different diameters on the bearing face etc is what you are worrying about, huh? Should be OK. Get OLN dimension right though, no excuse for getting that wrong, get washers/ally spacers as appropriate.
My experience suggests that you should be able to get away with the cone being-more-or-less the same size- I've not had any fatal problems with mixing and matching- fractionally different diameters on the bearing face etc is what you are worrying about, huh? Should be OK. Get OLN dimension right though, no excuse for getting that wrong, get washers/ally spacers as appropriate.