When the contract from GRWBSC came in, it mentioned nothing about required or even preferred technology.

Depending on the nature of your client's previous dealings with its client, could it be assumed that this project would use one technology or the other? If not, I'd probably say "In the absence of clear client specifications, I reserve the right to use the best tool for the job." Otherwise, I might worry more about the ethics.

It sounds like you've solved the problem in a simple way. If that's not acceptable, I certainly wouldn't recode the project for free.