Alignment shop says they can't get over 1 degree positive caster on 73 Scamp

If the toe from the shop is listed in degrees (most are now) it may actually be pretty close to 1/16" toe in. Converting from degrees to inches depends on the hieght of the tire, but unless your tires are really tall or really short it's likely you're not too far off 1/16".

As for the rest of it, totally agree. No reason you should have positive camber with radials, and that is effecting on much caster you can get. And finally, your alignment shop isn't great.

Most of the big name tire and alignment shops will only use the specs in their computers, which are factory specs and are for bias plys, which are incorrect for radials. Not sure why so many shops have a problem with these cars beyond that policy though. I mean, you literally just have to turn the cam bolts. It's so easy. If the ride height is already set that's all there is to do besides adjust the toe and that's just like every other tie rod car out there. The method Jim listed is how I start mine as well, I do all my own alignments now. With stock bushings you probably won't get too much more than a couple degrees of positive caster, but that does depend on your ride height. Even with the offset bushings most cars won't get to +4.5, but you should be able to get well into the 3's to maybe +4. I'd say if you really want more than +4* caster you'll probably need to go with tubular UCA's.