Question for the group

Hi everyone, I have a question. I have a 16" mirror from an old M..de Dob and I wonder if it's possible to drill a hole in the center and use it to make a cassigrain scope. No corrector plate. Truss design. I'd like to eventually mount it on a GEM and use it for photography. Assuming this is possible, what size secondary should I look for?

Any comments would be appreciated,
Thanks

Gary Pakalski