I had a good look at Jacob's saw yesterday it looks to be the same vintage
I'd have thought the damage on yours Bob relates to use of the machine when the table being has been tipped at an angle.
I had a gander underneath & it's the same arrangement.
It got me wondering as the metal is quite thin at the arched plate whether it was designed like that to allow what has happen to yours, on angled cuts the blade can have a tendency to wander, better cutting into thinner metal material rather than thick, it would also explain the arched shape 
Personally I'd leave well alone, there doesn't seem a great deal to work with re opening up for a removable plate, with a possibility of the table deforming when material is removed & it's not like they will ever be a "pretty" machine, particularly this vintage. That said having used this particular saw for over 4 years now it's certainly a workhorse & whilst not having the whistles & bells of modern machines, it still a damn good saw.
I'd use it for what it is, a good tool with signs of a hard history :yo:
