I'm really puzzled by the internal thread in the gudgeon pins. Don't recall seeing anything like that before, and can't see any purpose to having it there, especially if they are pressed in.
The brass ends of the pins look to be very big in relation to the pistons and con rods, so I'm wondering if they are just end caps or bushes? Something like this: https://blog.wiseco.com/what-are-wrist-pin-buttons
Could the brass ends be externally threaded too, and held in place with the split pins?
The internal thread could be there to facilitate installing them. Not sure how they could be got out if they are threaded though?!?
Worth investigating before you try pressing them out.