[142 Guy]

It occurred to me that the Amazon has that 'interesting' arrangement where caster is adjusted by two means:
- inserting shims between the body and the cross member at the rear attachment bolt
- inserting shims at the upper wishbone attachment point

Rustinmotion had previously alluded to this. Shims between the body and the crossmember are to be equal so that the crossmember is not distorted, so presumably this makes an equal change in caster on both the left and right. If you have differences between left and right caster values you use the shim differences on the upper wishbone attachments to correct for differences between left and right. The service manual is not explicit on the priority of these adjustments for setting alignment. Reading between the lines, I would expect that with equal left and right (or no) shims between the crossmember and the body, you would then adjust the upper wishbone shims to get equal (but probably incorrect) caster on the left and right. You would then add equal (left and right) shims between the body and crossmember to get the caster value to its final value. You then get to correct the camber value because caster adjustment is always done first and if you have used the wishbone shims to adjust caster you have automatically screwed up camber. If the mounting bolt at the upper wishbone is seized up, it will either be very difficult or impossible to correct the left to right caster problem and impossible to correct camber on that side because camber changes require equal shims under both attachment bolts. The left to right caster problem should not be causing your 'floaty' issue; but, getting them balanced should make it easier to figure out what is going on with your steering.

I expect that most alignment shops will not be familiar with the two caster adjustment process for the Amazon so if you get alignment set by a shop you will probably have to have a discussion with them about the process. They probably will not want to do this for a flat fee because the business of having to jack the car up to insert the shims between the crossmember and the body , drop the car and check and then repeat if necessary is something that modern alignment jigs (that I have seen) are just not set up to accommodate.

I am still left wondering whether the signs on your caster calculations have not been flipped. Negative caster does make for light steering and if your + 3.0 / 4.5 deg were actually - 3.0 / 4.5 deg this would turn your car into a squirrel chaser at higher speeds. Grocery shopping carts run with negative caster which makes for easy maneuvering around the aisles; but, notoriously unstable at speed.