Find a vertical "top dead center" on the wheel/rod boss, like a gasline motor's piston, mark that maximum height postion TDC#1, mark on the wheel o.d. ANYWHERE, and in align the other side to it's TDC#2 (a 90° easily arrived at being the maxium distance of movement left or right from the vertical reference I.e. just like verctical but measure sideways; Maximum iis the goal, not a certain number ). With TDC#2 mark aligned the mark for TDC#1 must still match up. You could substitute/add in some math too of course.
I take it they aren't splined? With splines I always found it pretty easy.