I would agree that if what you have is an Airport 25, it would be well worth holding on to.
 Noticed your posting and it struck me as challenge to find info on this one. Easier said than done, not much info out there.
 About the only thing that I have found so far is that the serial numbers that I found in my information agree with what you have. 
 In 1937 the model 70 serial numbers started at 300634 and ended with 302084, for a total of 1450.  
 If I find more info I will pass it on to you.