Scott:
I do not know which part you copied to start your own part, but there is a difference (probably more than 1) between your part and the ArchiCAD part. Under the parameters in the ArchiCAD part there is a variable called "GS_ShowDrNo", in your part this variable is called "GS_DrNo" (see attached image). When I changed your variable to "GS_ShowDrNo", then drawing number appeared, as this is the variable called in the 2D script you copied. I was able to figure this out by working backwards through the 2D Script, but this illustrates the problem of trying to copy code from one part to another. This is particularly true of the parts that use auto referencing, as the variables are critical to their operation.
Again, I would recommend starting with an ArchiCAD part that has this working correctly, then starting to change individual graphic elements to your taste, so you do not have to work through the more complex parts of the auto referencing code. Simply copying code from one part to another runs the risk of these types of problems.
HTH
David