Here is the metaborate formula indicated in the Mule Team link from Formulary:
They refer to it as Dihydrate.
Interestingly Formulary also sells Balanced Alkali as a different product. I assume balanced alkali is Kodalk which would be the typical octahydrate form called for in developer formulas. I guess I'll have to ask Formulary.
Basically this all concerns a few experiments I wanted to try with a few typical versions of split D23-type developers. I've always stayed away from mixing my own developers but just want to try a few things for experimental purposes. One formula is the Stoekler version which calls for 10g/L Borax (assuming decahydrate) in the second bath, and the other one is the Adams version which calls for 10g/L Kodalk/Sodium Metaborate in the second bath, and that's the one where I'm not sure what type of metaborate to but in the second bath. I'd like to avoid overcomplicating this with conversion formulas etc if possible.