I did top hat spacers a couple months ago. Rears are easy, just make sure you have your jack in a good position, once the shock is out nothing is holding the axle up, so you can't adjust the jack position. The fronts take longer because of the bars and taking the upper arm out of the knuckle...
How do you attach to the floor rails? It looks like you have holes in the rails so I'm assuming bolt/nut. Do you need to attach accessories to the rails then mount the rails to the truck? Or is it easy to access the nut underneath the rail?
I tried to swap my swing out case from my gen 5 to my gen 6. Both mounting brackets were significantly different. I was going to try the same thing as you, but the depth on the larger bracket where it makes a 90° bend was too different and could not be fixed with just a new hole. I'm not sure if...
On our trucks if you buy a topper from Ford, they will install the J-braces because they know the bed can't handle the weight. Ford knows its a problem and sells a solution themselves.
I could be wrong, but I doubt that Toyota is installing this type of brace on Tacomas for those that purchase...
This really isn't that crazy. They sell bed stiffeners for most trucks. On the F150 Raptors if you do a ton of off-roading the bedsides will actually start to separate if you don't have these bed supports. Definitely not comparable to the J-brace issue