Mustafagander
Access to the NLG on the B707 is from the avionics compartment, via the hatch in the flight deck floor, behind the left hand seat, where you would have sat if you had a command rating and to your left if you were a FEO, not sure about the pressure panel, but there are viewing windows to do a visual check for down and locked. Also behind the NLG housing there is stowage for the "Johnson Bar". This was used as the last ditch effort to lower the gear when you couldn't get it down hydraulically or by the manual release handles on the on the flight deck floor.
All the 707 gear pins that I have ever seen looked nothing like the one you describe, they were all of the large round "Pip Pin" type with a big red "REMOVE BEFORE FLIGHT" banner usually unreadable due to being covered in oil.
I have heard the story of the Load Master, Flying Spanner, Flight Engineer, whoever was telling the story, of how they managed to open the external avionics hatch just behind the NLG bay (which can be opened from inside as well) and stretch out of the aeroplane and remove the pin in flight. Not sure if it was really possible to reach the pin from there, as I always made sure I removed it on my walk round, so never had to try.