Removing Cam gasket
Hi it is possible (just) you need to remove any wheels from the cam along with any covers see how much clearance you have between the cam and outter circle of the seal .
You have two choices without removing the cam of course (which is by far the easier)
1: Get a long thing punch and with a soft hammer (copper or rubber not dead blow or the three pound lump hammer in the shed) and gently tap it, by tapping (not hitting) the seal will offset once it's done this you can the simply snip it and remove.
2: Get a 2-4mm drill bit with a slow drill (preferably hand drill) gently drill a small hole through, with something to make a hook (like an old metal coat hanger if you can still find them) gently slip the hook into the rubber hole then as above simply offset it and snip.
If the seal backs into the head it shouldn't be a problem if theres enough space simply snip in situe and remove. Replacing is easy too. If it's a rubber lip make sure the inner lip doesn't roll over itself or you will have oil leaks.
By now you've probably already done the job but I thought I'd just add a comment.
Charlotte