I you do a search here on APUG you'll find times I posted using original Ilford publications as a reference. However, I'm not sure how useful they'd be. Your HP4 film is certainly pretty old (decades). I had very little luck with 25 years old HP5 (stored at room temp.), exposing it at ISO 25 seemed good, but the basefog was so high, that I could hardly locate the frames on my roll.
I would suggest Rodinal 1+100 1 hour stand development, but others will have their own advices.
Post a picture to see how it turns out.