Thanks for posting these links, Sandy.
Referring to my post above to Matt (#15) I surmised that the mating element on the TSA series was BK7 as its time tested, readily available in uber high quality, and mates well with FPL53.
I was suprised in reading your post that in fact, the TSA mate is BSL-7. I was wondering how I could have gotten this wrong as I was not at all familiar with BSL-7 as a mating element to FPL-53. I did some additional research combing through some glass catalogs archived on my home server and found this Optical Glass Equivalents Table. It can also be found here:
At least I can sleep easy tonight knowing that I was not completely off-base... BK7 is the Schott equivalent to Ohara BSL7.
It appears that your memory served you well.