Nice find indeed!
I expose fresh TriX sheet film at 200; I'd try one of those plates at 100, give it standard (by the book) development (to minimise any base fog) and go from there.

Expired film can be very useable, I got very lucky and acquired some 8x10 TriX that expired in the late 80s, I give it from 2/3 to one stop extra exposure ( that is, 100 or 125 ISO) and standard (for me) development - I get no base fog and it behaves about like fresh film otherwise.