[Chrysler300] 1962 H - Bucket Seat Hardware Question

After a long, long, long, long search; I have obtained the missing drivers side bucket seat Adjuster / Tracks for my H restoration.

In looking at how they bolt on to the base of the bucket seat frames; I see the following set up....One for each side of each bucket:

STUD (5/16-24) - This enters the base of the bucket seat frame at the backside of the seat and is held on by a 5/16-24 Nut (a Whizz Lock Nut with that built in washer to the nut, similar to this: https://moparplus.com/1840-nut-mopar-a-b-c-e-body-seat-nut/ )
SQUARE BOLT HOLE - This bolt enters the base of the bucket seat frame at the frontside of the seat. The Adjuster / Track has a square hole, for what would seem to be a carriage bolt (probably 5/16-18 OR 5/16-24). That bolt screws into the seat frame; which has a fixed nut.

My question is....IS IT a Carriage Bolt or just a regular bolt? In my experience; carriage bolts slide into their square home & stay affixed, while spinning a nut on to them. In this case, though, one cannot spin a seat frame on to this bolt :)

And Finally -

Anyone know if the factory painted the Adjuster / Tracks gloss or semi-gloss black?

Thanks!

Matt Allyn