Sorry I can't help you with entry, but I agree it is a great looking survivor. According the the information I have, that pump was the 4th pump built in 1949. The serial numbers span from 18445 to 29711 for the model 996 in 1949.
Yes the buttons are actually the end of a cable( like a choke cable) That when pushed releases the latch that holds the doors closed The lock between them places a stop across the cables so they can't be pushed You will need to drill the center of the lock out so you can turn it to move the stop across the cables If they won't push after you have done that then the cables are probably froze up.
A key will allow you to turn a plate which access the cables through the holes on each side of the lock. Press the ends of the cable just inside the holes to release each door at the top. The doors just lift off once the cable is pressed.
Update. I was able to get the doors off by going through the top and using a pry bar to release the doors. Boy, those screws in the top did not want to let go. Thanks for the help, I’m not sure I would have ever figured that out. I attached pics in case anyone else can use the info.
how has your restoration been going? I finally got my 996C door off the other day (I ended up having to cut the latch at the top to release the door) and am going to start restoring it. Any plan on gutting it? Thats a decision I am struggling with right now. Also wanted to ask if you had a lead on rubber window seals?