Welcome to the forum.
If you have as standard pickup truck the easiest way I know of to identify the model number of the truck you have is by the number of lug nuts and drive axles. If it is an unmodified Chevy and has 6 lugs it’s a ½ ton which would be a C10. If it has 4 wheel drive it would be a K10. If it has 8 lug wheels it would be a ¾ ton which would be designated C20 or K20.
A C30 or K30 would be a 1 ton chassis, but I’m not familiar with specifics that would identify the details.
Another method to determine the original configuration of the truck is to run the VIN through one of the decoders. This will confirm how the truck started life. If you have trouble with the VIN just post it here and someone will break it down for you. Here’s one link that may help:
http://67-72chevytrucks.com/vboard/s...d.php?t=463671
I don’t have a photo to show, but there are two latches (one on each side) under the factory bench seat. There is a single length of piano wire that connects the two, so that operating the lever on the driver side unlocks both latches. If the passenger side won’t unlock, the connecting wire is either stretched, broken, or missing.