SF left VN by '72 except for a few guys who worked with Cambodian training and some other limited stuff.
The left seat sure sounds funny-or was it right seat?
I know a few guys who got to do a tiny bit of that, but I don't think it was common or significant.
I belong to a group of old SF guys who like to research such stuff and have deep resources.
If they had an ID especially SSN, they could check pretty quick.
There are factors of early SGF that make some ID diffucult, especially RVN service.