My son just finished a restoration on a '69 for his wife. He had no previous experience with body work, but had some welding experence.
He did not know that they make new floors for our trucks so he replaced the back lower half of the cab using a part from a donor truck, welded in new inner and outer rockers and a new driver's-side floor pan.
Some thing he learned from the experience is that it is better to have the front clip on the truck when welding in the inner and outer rockers to make sure they align with the front fenders and rear of the cab.
I have no experience at body work myself and have to replace both cab corners, inner and outer rockers and driver's-side floor pan. I have had some welding experience but a very, very long time ago and will either have to borrow a welder or buy one if funds allows.
When you are working on your truck don't hesitate to post questions on here and I am sure someone will help you. There are a lot of very knowledgeable and helpful people on this forum.
My truck is like I said earliner made up parts from 5 or 6 trucks. My son and I assembled it last summer. The short bed frame is from a '69 GMC I think, the running gear is from a '68 C-10, the cab and front clip is from a '67 C-20, the engine is from a 250 l6 from a '70 Chevelle, the transmission is a compound 4 speed from the original '67 C-20, the seats are out of an unknown year mini-van, the gas tank is out of a '71 C-10, the bed is a '68 short stepper (just bought it) and the tail-gate is from a '60-62 stepper. I probably missed some parts, but as you see our trucks can be constructed from many years. When I buy parts I have to remember what year and what vehicle they are from.
Here is a picture of the short step bed I picked up early last month. Of course it is not now on the truck in the picture and all the body work has been done on it, primered and wet sanded. I will try to get a picture of just the bed.
Good luck and don't forget to post pictures and to ask questions.
Danny