On your toe-in question you would want to measure at the points where your tires would actually be. That would be half the diameter of the tire from the center of the rotor. That would get you a starting point but you still need to put the car on the ground for all your final adjustments.
You cannot check caster unless you have the car sitting at the ride height. That means wheels on, All four tires on the ground and the weight of the car on the wheels.
Next time your pushing a shopping cart watch the "caster" wheels in the front. That is where the caster alignment word comes from. The stud that attaches the wheel to the basket's frame is mounted ahead of the wheel. The wheel is not pushing the basket the basket is pulling the wheel. You can stop, turn the wheels but as soon as you start rolling forward the wheels straighten right-out because they are being pulled along. That is caster. The further ahead the pulling point is the more caster your have.
Its easy to see caster on a shopping cart but its harder to picture it on a car. Caster is the center-line through the upper and lower ball joints. Its easier to picture what's happening on a straight axle like an old hot rod. The drawing I found below looks like a Mustang with a straight axle (Gasser)
Tilting a solid axle backwards or titling the center-line through the upper and lower ball joints backwards on your Mustangs increases the caster. Too much and it makes it hard to steer. Not enough and the wheels will want to wander around. Looking at the upper drawing below you can see that titling that center-line backwards puts the lower ballpoint out ahead of the center of the wheel so the ball joint is pulling the wheel down the road like a shopping cart
Looking at the lower drawing, tilting the center-line too far forward and now the lower ball joint is behind the center-line of the wheel and its pushing the wheel forward. There is noway it will stay straight.
On my hot rods you could stick an angle gauge directly on top of the kingpin because it is one solid piece going down through the axle and it has a nice flat surface. You could also stick it on the front of the axle and you could read the degrees of tilt backwards that way, which on a '32 Ford you would want around 5 degrees. Real simple to check on one of those cars. Its not as simple on Mustang because you don't have a nice flat surface to measure from.
You need a caster/camber gauge and you need to be able to measure when the wheels are turned 20 degrees special turn table plates. I'm not sure how else you would do it on a Mustang. The amount of times that your would ever use one doesn't justify having it. I get it that your trying to do everything yourself. I do the same thing. I was lucky enough to buy all the equipment out of my friend's, families automotive repair business that had been there since the 1960s. Tire machine, computerized tire balancer, brake rotor and drum lathes, valve grinder, hydraulic press, ignition scope, distributor machine, battery/alternator tester and the alignment tools. I have a bout 15 cars to restore and I like doing everything myself. So eventually I should come out ahead buying all these tools. If I live long enough?
