These RPM files seem to contain only one 32-bit binary file; brcupsconfpt1 is the name. Source is available for this, and a simple “make” command in the proper directory built a 64-bit binary.
I'm going to try substituting my 64-bit binary in the rpm2tgz I created.
But, I'm still not happy. The cupswrapper script Brother provided is very ugly. I'm not sure I will install it as is. I will update this with my results.