Camshaft wont fit

There are two plugs - one is a single concave cap - you put it in place against the step with the concave side facing the camshaft and then expand it by using a hammer to dimple the center in. That's the older design and the one I like most. The other is a larger plug- looks kind of like a freeze plug but has an outer concentric "ring" on it. It installs like any other core plug but does not expand. If that's in backwards and driven all the way to the step then the cam would more than likely hit the center of it. IMO it also doesn't seal as well - so I tend not to use them. maybe someone has a picture of the new vs old designs - I don't have any handy.