Bob,
I'm also unable to give a direct response but I did replace the driver in my Icom SP-23 unit (which looks to be a similar physical size to your speaker) with a Phonema driver. The internal quality of the SP-23 was very disappointing, with poor quality components and terrible construction. The original driver developed an intermittent scrape/rattle which sounded like debris trapped between the voice coil and magnet but which eluded my efforts to track it down. The replacement Phonema driver was a better made unit - heavier and better finished but not much discernible difference acoustically. However, I considered it a good deal given its quality, price, direct physical compatibility, and ready availability.
The baffling in the SP-23 wasn't too bad and I wasn't convinced that any extra was going to do much good in improving the communications audio. To hear what sort of changes might be expected I tried various amounts of medium density wadding (left over from my transmission line speakers!) but never managed to convince myself that it improved matters. In the end, I just ordered the replacement driver. However, it's a simple matter to try some extra wadding if you want to experiment.
The only residual problem I have is that the switches on the SP-23 filters and input selector are quite noisy even after having received quite a bit of attention. But it's tolerable with a bit of regular toggling.
73, Peter.