I'm trying to quantify the drift/lead/pull.
If you simply let go of the wheel (be ready to grab it back of course) does it immediately go right, or does it go straight for some period of time?
Because of the crown of roads cars go right unless the road is differently crowned or the car is tuned to lead up the crown, which obviously makes it lead left when the crown is level or revised.
When i was doing alignments we tried to set them up to lead very slightly up the crown, they were generally more adjustable then though. Also all of us could immediately discern the typical tire pull from an alignment pull on a test drive. Not to say there were not atypical tire pulls but probably 90% of them you'd drive it and instantly go "that's a tire".
I would try switching the tires around, i would caution however that although it's counterintuitive it's possible (but not common) for a rear tire to cause a lead. GM once had like a 12 page TSB on pulling/leading and half of it was moving tires around. I'm sure there are similar more contemporary ones.
Hunter does make a balancer that can calculate the amount of lead a tire is likely to generate, combine it with the alignment settings and generate a position for least propensity to lead. Finding someone able to and willing to use for a a reasonable expense may be difficult.
It may be helpful to move tires around and record the change or lack of change to be better armed for a shop.
Edit: I'm also confused the the tech did not want to move the cradle/subframe - is it extremely elaborate with many attachments? We used to do it literally daily, if not multiple times a day. It that were a w body GM id have had it perfect just by sliding the subframe ....