Just a personal preference for me is a snug (good old fashioned expression) fit rather than a tight interference. This helps assembling the gears, shafts and selectors before fitting the end cover with a touch of gentle rubber mallet persuasion on the cover while holding the selector in the correct position with the dots in line. A very light rub with a fine emery cloth will do the trick, measuring the shaft diameter so that you don't overdo it, we don't want a lose fit.
Alan