One isn't going to need a longer pushrod than the other.
If you are talking about adjustable to nonadjustable rockers, then they are different.
If you are talking about adjustable rockers with either hydraulic or solid lifters, then it's still a different pushrod. That's why there are 3 off the shelf part numbers for pushrod. One for nonadjustable rockers and two for adjustable rockers.
Unless you have corrected for geometry...then the length varies.