Your comment about cards on bicycle spokes mirrors my thinking exactly, in fact I used the same analogy myself. In any case it's easy to remove and plug. I got rubber plugs from my local NAPA store for $1.25 a piece. The firewall plug turned out to be an ideal place to run the sending unit wire for my Autometer oil pressure gauge.
How much oil pressure do these motors make??
My 2004 Marauder makes about 100 PSI cold start then settles in at about 25 PSI hot idle and around 50 PSI hot cruise (2200 RPM's)!!