Tom, The 45-70s I stuck were deprimed seperately (Lee Universal Decapper, very handy), no decap rod or expander button in the sizing die at all.
I suggest that if it works for you, great, but think beforehand how you will have to remove a stuck case (always a possibility anyway, but we rarely deal with it) from a die, some are much worse than others.
For instance, if a rim edge pulles off you can rotate the shell holder to a 'new bite' (still no guarrantee). If the decap rod and button are in there you cant just unscrew it and pull it out so you can rap down with a punch on case.
This 45-70 die had a 10x32 (?) hole only, no room for a punch, and when the rim/heads came off it required removing the die, chucking in the lathe, CAREFULLY tapping the inside of the case with a tap that wouldnt bite into the die, removing die from lathe and mounting in a die plate on the bench vise, screwing in a bolt, setting a Cresent wrench on the shank and against the underside of the head and hitting it with a hammer.
More than a fair bit of messing about, that! And THREE times.