Rudy's has the 25 cent denomination CLEAR chips:
http://rudysdeals.com/williams,dotmation,clear,u-3You can contact them thru their website and ask about the nickel version and other items:
http://rudysdeals.com/index.php?route=information/contactI thought the optics boards below the coin acceptor/comparitor stayed the same no matter what coin the machine used, but maybe not (see below). I think the front part of the coin entry head stays the same but the back portion is different for different coins. They are shown as items 9 and 10 in the drawing below.
The manual does show 2 different optics board sets, one set is called a quad, the other hex, meaning there are either 4 optic or 6 optic sensors on the boards. There isn't any other info so not sure when one board would be used instead of the other. Perhaps the hex board has more optic sensors for larger coins that pass thru, or maybe it has them spaced closer for small coin (nickel?) use. If you convert the machine to nickels you can wait on changing the optics boards, see if the machine plays ok, if not then you can change the optics.