Since you are planning to replace the sides of the white bed with the blue sides it seems like fitting the bed will be a little easier. Still a lot of work but looks like it should turn out nicely.
I am thinking that it will be a little easier.... my plan is... (open to anyones thoughts on this... been trying to figure out how to do this for some time.
to pop the front cap off the new bed, then cut it down to whatever length that I want on the 80 frame. I want decent departure angle, knowing that I will put a 2" receiver under it somewhere. I won't have a tire under it, so thinking I will cut the frame back some. Once I rough out a thought, I will compare it to stock 45' shorty bed. I added 3" of length to the tub since it was in your shop, so there is that as well.
Once I nail down bed length, and chop it down, make bed mounting points and bolt it down, then cut off the current sides.
Then take the blue sides and modify the wheel well to be in the middle of the tires, likely have to cut and move the wheel arch and then cut to length. Note: it appears the wheel arches are patch panels recently replaced. Really heavy duty and really straight!!!!
Question for @47coeman Do I need to do anything to keep the bed floor all flat and square? I was thinking that once I mount the "new" bed down, that I should be able to cut it off and put the new one on without any temp reinforcement... thoughts?
Go to 16 seconds and see how they removed the bedsides....