Curb weight is the only way to get the alignment right.  Took our's a week after it was finished with no problem.  If you don't trust the guy to keep his belt buckle off of the paint, you sure can't trust him to get the alignment correct, IMO.  To begin with, is he familiar with alignment on these old cars.  We have a guy here who was into old 'Stangs and owned his own alignment shop for years.

BB

I have been amazed at how much the alignment changes on these cars with weight change. I have gotten to the point that I put enough bags of softener salt in the drivers area to equal my weight since 90 percent of the time I am alone in the car. Then I do the alignment with a piece of firring strip through both windows clamped to the steering wheel with it straight ahead. I do a four wheel alignment then and it drives so nice. I have had to heat and bend some of the steering arms to get geometry close enough so the car will actually go straight down the road on a couple of cars that had been put together from misc parts. I assume the spindles were from a close but not quite perfect application. I know one was a Granada swap.