A couple of issues in converting a percussion Sharps to a 50-70 center fire cartridge is =
First, the barrel bore size difference from .54 to .50 cal.
Second, is to getting the spent casing out of the chamber.
Third, is a modified breech block from the percussion to center fire.
Fourth, is modifying the hammer.
Each of these operations require some very specialized tooling to initiate on this type of conversion.
I hope this may offer some help?
My best,
Blair