35 and first series 36 truck seats may be somewhat alike. 36 second series, 37 and 38 seats are generally speaking are the same.
The 36 seat bottoms are very similar to the 37 and 38 while the back of the seat is the same. 37 and 38 seats are the same with the one difference that the 38 front right side cushion has a rise in the frame of the seat for the gas tank neck to clear the seat. While the 37 gas tank filler is under the seat, the 38 right front seat will fit the 37 truck, but the 37 right front seat will not fit the 38 truck. In the meantime, the 36 will fit the 37, because the gas tank on a 36 2nd series is located in the back of the truck under the bed, causing the 36 seat to fit the 37, but not the 38 because of the gas tank filler tube.
Yes, I know it sounds like a bunch of jibberish, but that's pretty much how it is.