Washer = good as long as you use a proper metric grade bolt (i have 10.9 rated in mine), one thats long enough, and get correctly sized washers (i'm using 3/8" hardened washers).

stock size is M10x1.25 pitch by 45mm long. For me, 2-3 washers that were exactly 1.75mm wide each, corrected for 0.4-0.6 degrees or so. I cant remember exaclty right now, too late to look for my alignment sheet.