Instability Question

I have aften wondered how alignment shops can do alignment on muscle cars with fatties on the back and skinnies on the front using factory specs?

Do they have a general set up for these types of cars with lotsa mods and different sized wheels?

I really, really lucked out and did my own alignment in my garage using my eyeballs and measuring tape.
My car tracks straight and the tires are not showing any strange wear.
I guess I lucked out, but I used to do alignments at the dealership on factory cars only.

I would like to know where to go so I can get my car professionally dialed in.