May want to try another caliper for comparison. If you have access to a lathe you could turn it down but you couldn't add to the first stage. That said I think you could still get accurate grease readings.
Off hand, I say you lost 400 rpm and ran out of motor because of the higher pitched prop..If your engine could still generate the 4800 rpm you would go faster..
Put recommended amount of oil in, the dip stick is a joke , if you don't have oil in the bilge and the motor is not pumping it out on the water your good.
I don't know your situation but couldn't you core it as far forward as possible and then run solid glass just for the edge that tucks under the forward section.?
