I created an Access database years ago with information similar to that PDF. The one difference that I had was that I put in purchase price rather than replacement value. My reasoning was the the purchase price was was a concrete fact, while the replacement value would likely change significantly over time. The replacement value for a lot of guns went up significantly during the mid 90s, then dropped somewhat a decade later. As we all know, it also depends what state you happen to be in at the moment.
I moved it to a MySQL database a few years ago and, since I had a digital camera, added a field for photographs of each item. I don't keep just firearms in the database, since a lot of the glass I've got on them cost as much or more than the guns.
Ken