This is tough. Most probably this opener was manufactured by one of the major companies and then branded for Edwards. Only someone familiar with older openers would be able to tell. Most likely if it is as old as you infer it would be an older radio frequency and would not work with modern electronics. I would bite the bullet and replace it with state of the art electronics and safety features.

I have a circa 1960's garage door opener . One of the plastic gears teeth have worn away . It just now gave out this past week. MOD# 139.664956 Part# 81B11 . My question.
Is there anyone that deals in or scavenges old GDO parts in the Austin ,Tx. Area?