Lots of people have installed ARP head bolts or studs without pulling the head. Just follow the torque sequence and pull that bolt and replace it with the stud and torque to spec, then move on to the next one. 9 out 10 times you can pull it off and not damage the head gasket.
It went in pretty easy, but I can't tell the difference between the pioneer and the stocker, too many years of listening to hard rock and metal, my ears are shot.
Get the LMR versions, they look the same and are lighter and you can get them in a 19x10 square and run a 285/35/19 tire. the ford performance wheels have a unique offset to run a 305/30/19 in the front, and a 315/30/19 rear. That tire is too much for the street and they are not cheap either...
I just installed the same catch can on my 23 mach 1 on Saturday, and I have the stock plastic coolant tank. My can was hitting the tank also so I had to bend the bracket a little to make it work. There is a little room between the can and the front of the head, enough that you can lean it back a...
I finished up the header install on my 23 today and since ford changed the O2 sensors sometime between 17 and 23 stainless works includes both types of extension cables. Back when I put headers on my 17 I only needed to use the short extension, and I have the long and short leftover from the 23...
I didn't see this mentioned but the cam cap bolts are TTY so they would need replaced also along with the phaser to cam bolts. Good news ARP makes reusable bolts for the cam caps, cam to phaser and the phaser itself.
https://lmr.com/products/2015-mustang-camshaft-valvetrain#21790
I've never driven a S-197 based GT500 but the trinity engine was the peak for that platform. They were 662 hp stock for 13-14 only. But like you said the tech was dated even when they were new.
My suggestion, get a mach 1 equipped how you like in your favorite color and throw a whipple on it...
The OP asked about the gauges being the same as the 2020 gt 500, All GT verts are premium cars and on the 18+ you had to get a premium car to get the digital gauge cluster. If you also want the center stack gauges, just a performance pack vert.