Totally normal for an early car such as yours.
The outside fuel door was added at a later date.
this style aftermarket fuel neck is available from Hall Pantera. I am pretty sure it does not have a screw on cap but utilizes the old-school style of cap
this style incorporates a screw on cap. I do not know if any vendors are currently selling this style.
converting to an outside fuel door is a time consuming and expensive modification to add to an early car. And that assumes you can actually find all of the parts and pieces that are required.
Larry