Old Ilford Ortho film

I just receive a box of 8x10 Ilford Ortho film, not the newer + variety. I have ben told that the ISO is 20, but that is all that I have been able to glean. Ilford has not responded to my request for a data sheet. Does anyone with experience using this film stock have any information they can offer?

If it's the stuff in the red and white box, EI 20 is prolly a good place to start? I shot a lot of it in the '80s and '90s in 4x5 D76 1:1 was my choice and it worked well. Has definite ortho tonality

Yellow Springs 2 Norma Ortho D76 Arista Multigrade by Nokton48, on Flickr