...I'm thinking about mounting something on the firewall...
Maybe a good time to mention that the top of the firewall is usually considered the best place for an oil breather (if you were thinking about putting something else there).
Mounting a breather high makes it easier to give the output tube a steady, downhill run to wherever it's going. And a breather with enough volume to work well takes up more space than is available just about anywhere else in a Speedster engine compartment.
My VS has about five inches between the firewall and fan shroud, and the oil breather takes up about half of that.