I've never seen anyone say what glass types Televue use in their scopes. Al Nagler never mentions it, and I have never seen it mentioned on any astronomy forum.
With that said I think I have found the design. A patent search using Albert Nagler in the search field comes up with the following
patent.
It appears as though his petzvel scopes use BK-7 (abbe 64.2) and SF-12 (abbe 33.8)
Considering the high esteem that these refractors are held in, it proves that you don't need FPL-53, or even FPL-51 in order to produce a well corrected telescope.
I think that patent has expired now as well, it was filed in 1983 and they only last 20 years, so the Chinese can start making them now
