The 25-35 is closer dimensionally except for the rim, which is 0.020" wider. Double-check your chamber with a caliper to be sure it will accommodate the 0.526" rim? The Zipper and 30-30 are 0.506" nominally. Whichever case you use, it will need to be sized down and trimmed to the shorter Zipper length.
A number of makers sell forming dies or can make you a set.
RCBS has them in two sets. One for starting with the 30-30 and one for starting with the 25-35. They want $250 for either set. In an unusual order of things,
Redding has a set for a little less, but available only for forming from the 30-30. Three dies are needed and they run $75 for #1, $75 for #2, and $62.40 for #3, for a total of $212.40. Redding has the edge on fit and finish quality, IMHO, so that's the way I would go in your shoes, despite the extra work of forming the 30-30 case. But you should check your chamber rim recess and the availability of the two kinds of brass and decide for yourself.