The string method is basically the same idea as yours but without the steel studs. (I use chalk line for string)  I wrap the string around all tires and measure each wheel front and back and make the appropiate adjustments. use a 1/32nd scale rule and count the lines.

Sorry I'm doing this trying not to get caught. Plenty of honey do's pre holiday. Yes the toe gauge reads in minutes and degrees. I measure camber in degrees as that's what my gauge reads in. Getting the toe correct and taking out all crab is a win win. I so much enjoy what I do I hope it shows in my work. Steve (CTR) 

So I just had to look it up and still not clear..... I'm sure you're waiting for someone to ask, so I will

1 minute is 1/60th of 1 degree?

60 minutes being 1 degree?

"I run about 5 minutes toe in and 1/2 degree neg either side at the rear."   Why the mix of minutes and degree...is the latter the camber

Yes toe out at the rear, and that is toe out at the front of the rear tires. If you are using a Dunlop Optical gauge it will tell you it's toe in but you can figure that out. This gauge is very good so I can dial them right in. While people talk about the string method I have never been able to figure that out. I have two 12 ft. steel 2X6 studs. I place them on buckets along each side if the car. With Dunlop gauge I set front at zero. Slide the studs up against the front tire touching front and rear. Then attach cross menbers at the end of the studs. Clamping them parallel to each other just touching tires at front. This leaves a space between the studs and the rear wheels. Measure distance to front edge and rear edge of rear rim. Should tell you which side is what then you work from there. 

Zero or even a little toe out rear is fine if you know it and want to drive a loose car. This car is for a young lady and I believe is her first classic mini. I felt a little more stable turn in would be best for her needs. I run about 5 minutes toe in and 1/2 degree neg camber either side at the rear of my car. Steve (CTR)

Edit: something else I learned, a new set of Yoko A 539 165 / 60 / 12 tires mounted on 5 X 12 wheels really hook up. I'm even thinking of building an autocross car and using those tires on a set of drum brake offset 6 X 12 wheels. It will take some fat flares to cover them mounted over disc brakes. I have an old vintage/hill climb 67 MK 1 shell with the wings opened up front and rear.  

So it was primarily the rear toe out that was the problem on the freeway, right?  

I just shimmed my rear for straight ahead - it was 1/16" in before.  However since I'm using the string method, the rears are aligned towards the wider front - which would toe them out.  If that makes any sense.  

So perhaps I should measure the track width from the hub faces for front and rear, then cut the difference in half, then space out the rear string by that amount to get a perfect rectangle.  

Sorry I have not had my coffee yet and shouldn't be doing this anyway...

I recently worked on a 72 1000 mini. It had drums and a single 1 1/4 SU carb. After dropping the sub frames having them blasted/powder coated I rebuilt swing arms and front uppers. Converted to 8.4 disc front and spaced drums rear. Everything was replaced and installed. After centering the rack and setting the front toe at 30 minutes out I went for a ride. This was after setting ride height and even rolling it over the scales to balance corner weight. To my surprise at speed 55/60 mph any steering input would just about change lanes. I had spent so much time turning half a turn this side then that trying to get the setting I wanted with the steering wheel centered I thought I may have missed my set up. Back to the shop and put the Dunlop gauge on and sure enough it was right where I left it. Going to the rear I found the rear to be 30 minutes toe out as well. Doing some more checking showed right side was zero and left side wa 30 out all on it's own. I removed the rear swing arm outer brackets made some notes did some measuring and welded up the holes and moved the holes forward. Thinking that hard makes my head hurt. I was able to move the right side to 15 minutes in and the left side 45 minutes. After getting 30 minutes toe in at the rear I moved the front to 15 minutes out. I guess the rear would have been crabing but should run true now as well as being very stable on turn in and though the corners. The 165/60 12 Yokos are a very sticky tire when new. I'm thinking I need an auto cross car to try them on. Steve (CTR)