i know this can be tough. i started doing conversions a couple years ago and have since done about seven for myself and family members. there are some chainrings and cranks that are less round than others and although the sheldon brown method of centering the chainring on the spider will help a bit - it won't solve significant runout. its hard to tell ahead of time which cranks will have less runout. in my experience the shimano 105s and 600s were less round than the few sugino crank/chainrings i've worked with. i also hate to say it but generally the nicer the cranks/CRs the less runout you'll experience. in the end i realized spending a little more money to save myself the hours of hassle is worth it. plus i've thrown a few chains that were too loose too avoid binding - a big downside. hope that helps.