A bit wordy, but here goes:
Brad's Custom Auto in north Seattle has done extensive mechanical work on all 3 of our Mustangs. I would recommend them before anyone else. They have an in-shop dyno and can do just about anything. If you call them, tell them Sparky says hi. ;-)
Marysville Speed can be a bit pricey, but I've not heard any complaints about their work. They are about 3 blocks from my house, and the owner is my good friend's nephew lol. As per their name, they specialize in hot rods/race cars. They have an in-shop dyno as well.
Bel-Kirk did the suspension on my '66 many moons ago. I've heard iffy things, but nothing horrible.
Another friend, Scott Robinson, owns Northwest Pony Shoppe out in Snohomish. He did my '66. He's mostly retired, but chock full of information. He'll be at the swap meet in Monroe this weekend, as will I...I'm in building 400, space 56. Scott usually is against the fence along Highway 2.
Randy Sargent is a great painter/restorer, and charges accordingly. He replaced the cowl on my '66 in 2009, and the seat pans 2 years ago (long story). Very easy to work with, and not flaky as a lot of painters can be.
The good friend I speak of above is Neil Knutson. He's an ex Ford mechanic and known locally as the "Four-eyed guy" as he specializes in '79-'86 Mustangs and Capris. He goes to Scott's to help him out with mechanical stuff all the time. (And our shop, as we share a lawn with his house lol).
DO NOT, under any circumstances, go to a certain Mustang shop in Auburn. PM for details...but I wouldn't send my worst enemy there.
1966 Restomod/track car, 1973 Q-code Mach 1, 1997 F250 diesel, 2000 VW Beetle Rallycross car, 2010 Crown Vic (ex-City of Lakewood PD), 2015 Focus ST-2