Gevaert Ultra Panchro exp 1944

Here I have 2 boxes of 5x7 Gevaert Ultra Panchro anti halo safety film, expired in 1944. Originally sealed and in general good looking, no apparent moisture damage.

What would be the good EI for the start? And some developing times with D76/Rodinal/HC 110.
I am absolutely aware of possibilty to get only fog but anyway

At an absolute guess, I reckon 25 would be a good starting point. If you're shooting in a camera with a darkslide, you could stop down massively and/or put a ND filter on the lens (in order to get a long exposure time: meter for ISO100 and fiddle the aperture until you get an exposure time of 1s) then pull the darkslide out a little and open the shutter on B after 1s, pull it out a little further, after 2s a little further, after 4s a little further, after 8s a little further (NB these are total times, not sequential) - this thus gives you a 4stop range of exposures on one negative. I'd suggest developing with Rodinal 1:100 for an hour, agitate for the first minute, then wait and don't touch it until you pour the dev out.
Whilst this may give slightly flat negatives, rodinal doesn't excessively fog and stand dev works for pretty much any speed you care to shoot at.
Alternatively dev in HC-110 or something like TMax, Microphen, DDX which are all minimal fog developers for a guessed time.
Obviously, there may be reciprocity problems, but it'll at least give you a rough idea of the film's ISO.

If there is some fog, development for flat look won't rather help. Avoid Rodinal 1+100 in this case, try something more contrasty instead... HC-110 (dil. A / B) or Tmax should do just fine.