You could right click on the 32 bit DimPro synth in track view, there is an option "Replace Synth", where you would replace it with
DimPro 64 bit . . . but I don't think it will call up your old patch.
I've had this happen opening many old projects, but I've always been able to open it on my old computer to see what patch the older DimPro (or Rapture) was using. Do you have that as an option ?