On the PG, I ended up with a slightly different amount. I don't remember why. Since I had multiplied the formula to use 0.25g phenidone (smallest I was comfortable weighing) I think it had something to do with that. Anyway I had used a slightly different amount of concentrate to make 1 liter and the pH was slightly off. We had decided that I should have used the correct amount. I also used the 8 mol variety Sodium Metaborate.
I can report that the small bottle of concentrate is sitting on my shelf entirely unchanged from the day I mixed it. I can also report that I tried developing a few frames of homebrew emulsion (TLF2) in it and the contrast was quite low compared to D-23 or D-76 1:1. However, the contrast of that batch of emulsion was low anyway compared to other batches I had made, which are all lower contrast than commercial films.
I like the idea about dissolving the phenidone in alcohol and measuring it out that way.