I would probably put the bow on a very low brace for an hour or two(2 0r 3" max) Bracing height depends on length of the bow but is normaly 6 -61/2". If the bow is over 80yrs old as you say and now used for a v. long time it should be treated as new
http://www.bickerstaffebows.co.uk/advice.htm will tell you what to do.Oh and good luck be careful when drawing it there is a good chance you may feel the draw weight drop away like a compound bow and recieve a smack to the head or groin!!