I believe the cam is part of this equation as well. A hydraulic cam has a groove in the rear journal that has to do with oiling. A solid cam does not. I put a solid valve train in a hydraulic head, and I remember having to regrind a solid cam as well.
My disclaimer, and other experts please jump in here if needed. I did this swap a while ago and may be fuzzy on the details, but I think this is right.