Originally Posted by LATECH
Look at the back of the cab on the 08. You will see it is extended at the back of the seat area to make room for the aforementioned thickness. The cab on a 65 c 10 is a box. Straight up and down. Most likely if the seat goes in, you wont be able to fold the back down to the point that it is comfortable. likely will be straight up and down.Also will end up way too close to the steering wheel.Newer trucks are more ergonimic, older trucks .....not so much.
Also as mentioned, width will be an issue also.
I would recommend fixing the seat you have
If I recall, that vintage Chebbie had the gas tank behind the seat - hopefully the OP will be taking it out, replacing it with something under the bed and in a safer location. That would give a bit more room.
As far as tracks - they have plenty of adjustment for placing a seat. You just have to make sure you take that into account when placing the seats.
My biggest gripe with many new seats are the head rests with to me just look wrong in an older vehicle