Sorry, I misread your original description - these are stud-mounted, not shaft conversion, so the adjuster height on the stud is a variable (but not the same effect as rocker shaft or stand height) and pushrod length is definitely relevant.
Is the stud parallel to the valve stem axis, vertical, or other?
If it's not parallel to the stem, any height adjustment also moves the roller across the tip (tight = closer to the stud).
Your roller tip is already going to be about .059" too far across the stem tip just because of the BBC lever length vs. original (1.649 - 1.590 = .059), and any attempt to center this is just going to make an error somewhere else.
The short lever (pushrod side) has to be about .916" for 1.8:1 ratio, .054" closer to the stud than stock (the stock 1.7:1 lever is .970"). I'm not sure how much pushrod clearance you have.
