Why do you need to include Gencad files in your manufacturing data? (Who asks for that?)
I have never needed to include them and have had hundreds of boards made for me.
RS274-X Gerber files and Excellon drill data can be used by all board manufacturers, if you need to go to more information then you can include ODB++ for the assembler
or a CSV file with the xy positions & rotations etc.
Gencad (IPC-2510 series) was going to be the all singing all dancing interface between the PCB design and all other downstreem processes, fabrication, assembly and testing. As most manufacturers use Valor tools (now Mentor) ODB++ sort of took over as a defacto standard. There are some firms that use Gencad (Lockhead Martin comes to mind), and there has been talk in the past of incorporating Gencad and ODB++ into the ipc-2510 format to create a universal PCB design to the rest of the world interface. This has died down in the last few years, in fact it was 2006/7 when I last got involved with discussions on combining the two interfaces.
Sorry I cant give any opinion on your data, I use ODB++, and arn't au fait with the fromat any more. I have attached a link for all the IPC-2510 documantation, it is a free download.
**broken link removed**
**broken link removed**