Wandering through one of the area flea markets, I finally came upon a seller with some pens wrapped up in plastic bags. I saw this Pilot and thought it looked familiar, so I bought it for a few dollars and went home to check it out.
The pen is actually a Pilot Custom 74 pencil, with a plunger system that pushes the lead out of the steel cartridge.
The rubber eraser was used a bit and the end was crumbling inside the steel cartridge, but other than that everything works perfectly. The pencil uses 0.5mm lead, which seemed small until I started writing with it. There are no nicks or scratches on the barrel or cap, no brassing or wear at all, just some minor micro-scratching on the section. It's a great find, and a nice addition to my collection as I already own a Custom 74 fountain pen.