Wayne has all those part for the throttle available, if you can't find some used. I just sold a set for the early type on Ebay last november, and have seen some come up for sale now and then.
I know when Wayne first made those side covers, he made them deeper than original, to decrease the volume in the engine case to better promote the flow of fuel through the engine. He also provided 2 gaskets, just in case the fit was a little too tight. He told me some engine needed just 1, but some needed 2 for clearance.