Sounds like a plan. I sent you a PM. Here's what the specs say:
The MX 300 Nav/Comm is designed to replace the RT 328T, RT 308C, RT 328T, RT 328A, RT 528A, RT 328C, RT 528E, RT 328D, and RT 508A.
BTW, here are some pics of the VOR head. I removed and cleaned the glass awhile back and it's spotless:
