"Windshield bars have two bends."
The counter-bend in the front downlegs ("windshield bars") is crap. If you buy from them, request straight legs.
Here's a good primer:
https://24hoursoflemons.com/wp-content/uploads/2017/06/How-To-Not-Fail-Lemons-Tech_v3.5_040419.pdf
Spreader plates are a must! Otherwise it's just a show cage. As it says in the .pdf above, 24 sq in of spreader plate per tube end should be your minimum, and the kit has 6x6 spreaders, although 1/8" plate is a little on the thin side. If your target mount point isn't level, build a plinth.
If you're caging a street-driven truck, be sure and put the bars far away from your head. Your head is very squishy compared to a roll cage, and you're not going to be wearing a Snell-SA rated helmet while driving on the street.
You want your cage to fit the cab as tightly as possible. The only real way to accomplish this is to cut holes in the floor board for your main hoop and downlegs. You drop the main hoop legs through the holes you cut, mark where they go through the floor, pull it out, cut the excess off, and put it back in place with the spreader plates resting (not welded!) underneath. Get your halo bar in place, snug against the roof (account for the headliner if you're keeping it), and tack it to the main hoop. Then put your downlegs in through the holes in the floorboard. Mark and cut them, slide the spreader plates under them and tack them to your halo bar. Pull all your spreader plates so you can drop the cage down and fully weld it. Raise it back up, slide your spreader plates in place and weld them.
I've built one cage, but did a lot of study before hand, and had a professional who bent my tubes and instructed me how to install them.