I did both moves...
104.9 was the only frequency available for WRBB, though their D.C. consultant recommended 92.1 which I rejected because I believed that UMass had bigger aspirations then the 200 watt signal they were running from the gravel pit in Quincy at the time. Turns out I was right! There was some talk of installing a directional FM antenna atop the Pru for 104.9. They could have run as much as 15 or 20 watts towards the 105.1 in RI. It was rejected due to cost.
The original WRBB move was done when their antenna was still on the Ell Center. The station went off for the day so a 1 bay 104.9 antenna could be temporarily installed in place of the 3 bay 91.7 antenna. I provided a loaner Versa Count exciter tuned to 104.9 and on they went.
Later on, they moved to the existing transmitter site, using an RCA BTE-15A exciter I sold them as a transmitter. If I recall, the exciter was located in an elevator motor room. One day the room got up to over 120 degrees, the AFC on the transmitter unlocked and it went on a trip all over the FM band. They got fined by the FCC for that.
With regards to WBRS, originally they used an LPB solid state transmitter (it was a rebranded QEI with a meter panel). Their 91.7 antenna was a 4 bay horizontal Marti FM antenna. When they moved to 100.1, they installed a five bay Shiveley circular antenna. They actually dropped ERP from about 40 watts to 25 watts.
After a while, the antenna interbay wiring became damaged, so we salvaged the bays and got an FCC waiver to run 25 watts transmitter power into the top two bays. We bought a 30 watt Bext exciter for the main transmitter, and used the LPB into the next two lower bays for a standby system. The bottom bay was eliminated. The interbay wiring is all homemade by me-though it's identical to the Shiveley wiring for the 2 bay version of their antenna.
As far as I know, that's where they stand now...though they might have retired the LPB by now and replaced the Bext as main.