I was taught, during my engineering career, that stainless steel bolts are best for aluminum, always use some lubricant, and always torque to specification. Always make sure they will engage at least 2X the diameter of the screw, 12mm for a 6mm screw. I have found most of the tapped holes in the 750 and 550 cases will handle about 3X the diameter I am sensitive to the feel as I thread them. If there is an increase torque required to thread the screw, I stop and cut them down a few millimeters. I make sure to chamfer the cut end to remove any r
Zinc plated screws corrode in the case as most of us can attest too when we remove those with an impact driver and find the white powder in the threads. Takes a long time to corrode, but it is not good for easy removal after decades.
I was never taught to use a specific grade SS. Prefer to buy 316 grade stainless as they are readily available from McMaster Carr.
I put them in my 750K6 in 2008, no issue 13 years later when disassembled.