Is this a stock seat? 68 C10

[AllGoNoShow]

I'm having a few problems installing some aftermarket 3 point belts and am just curious if the seat I have in my 1968 is a stock seat or what. It has little nubs on the sides of the brackets which connect the seat bottom and back-the "nubs" have a bolt and nut on them(presumably to fold down the rear back part of the seat if its removed). The little nub is interfering with the reels for the seat belts. Looks like I will have to hack away the circle nub thing and somehow put some bracket in there to remove that fold down feature to get the reel to sit properly. Doesn't seem like anyone else is having this issue so now I'm curious if it has a non-stock seat in it. Pictures below. Let me know what you think.