What sort of grip and squeeze do they need not to shoot low left?
Not a textbook, do it this way kind of thing. The ONLY way to "get there " by shooting enough for total comfort and familiarization with that particular gun.
Get some comfortable to shoot ammo then shoot it a lot. Try different stuff. How you grip it how you pull the trigger and just as important, stand up and get off the bench bags every now and then. Benching is fine for testing ammo and such, but it is not how to shoot a handgun. They just plain shoot different when rested on a bench.
Most of my better single action shooting with a plow handle is done with a tighter grip with the bottom 2 fingers. Middle and trigger finger doing little
gripping. Trigger pull is straight back with just the distal pad on the trigger. Do some dry firing. Study the sight picture as the hammer drops seeing if it moves around. Try different grips and pulls.
Sometimes I use one hand, sometimes two. But if two it's only for gentle cupping support ,,,,,,,, no gripping.
The second I shove my trigger finger in to the second joint or grab the grip like a fist, groups go out the window. No such thing as cranking out the shots, execution of EVERY shot must be concentrated on.
Not saying it is the case. But taking a big ole single action to the range once or twice a year with a box of brutal , Ruger only beast loads will never get it there. Getting comfortable with it will.