Bro..I picked up a seat from a 1990 and slapped into my 62. I drilled out the two front bolts holes to be able to align it up and then just marked the rear location with a punch and drilled out...let me see if I have some pics
Here is my seat in my 62 that came from a 1990 Silverado. What I ended up doing is drilling out the two original bolt holes on the floor pan of the truck with a 1/2 drill bit. I then separated the seat from the frame and bolted it in place and marked the rear holes. Drilled them out and then put seat back together and bolted into place. I did use some 3x3 inch plates under the cab as washers.