nice find !
in the 1980s/1990s a box of tmx(400) 4x5 plates cost about 400$USD
you made quite a find!
they are probably still good, just do a test exposure at about asa200
and process in a strong developer .. if you have dektol i'd try that 1:7 for about 7-8mins
the only problem is you need PLATE holders
sometimes they are easy to find sometimes hard to find
and to process you willneed either a tray to process them 1 at a time
or a film/plate hanger and tanks ...
not too many bumps in the road though ...