How to make a 65 cm lens with a 20 cm hole in it for a Hamiltonian telescope? This answer to What (the heck) is a Hamiltonian telescope? Is this one? confirms that the telescope in the question linked there is indeed as described and that the first lens is a full 65 cm aperture lens, the second element is a full 65 cm negative meniscus back-silvered, and some corrector lenses are embedded= within a hole in the large primary lens.
Optically I can imagine that it might be possible to let the light transmit again through the primary and still compensate, and mechanically that seems more attractive than polishing a double-sided transmission lens with a hole through the center.
But apparently that's what's been done.
Question: How to make a 65 cm lens with a 20 cm hole in it for a Hamiltonian telescope? I'm thinking about issues including the following:

Is the blank cast with a hole already, or is it drilled?
If drilled, is that before the first side is polished, before one side and after the other, or after both sides?
After drilling does one need to anneal the glass again?

Glass can experience strain-induced birefringence among other things, so I am really interested in finding out how optical surface figures are applied to both sides of this lens with a big hole in it without causing optical problems within the bulk of the glass.


Image from this answer to What exactly is a Hamiltonian telescope? Is this one?
Drill or core the blank
(anneal if needed ... most likely not if annealed to begin with)
use pitch to glue a plug of the same material in the hole
grind, polish and figure as normal then remove the plug.