I think the letters HP do not refer to the horsepower rating. It just means its an "HP" block.
They can be viewed on the block from under the car on the passenger side.
I agree without at least a few good pictures and verified #s it is VERY hard to estimate a value. It could be worth anywhere from $9,000 to even $25,000, depending on how rare the options, condition, originality, color, etc etc.
Making your assumptions, I would say maybe somewhere in the teens, so....90% there....
I dont think so!
Anyways, keep asking questions, and good luck.
Hope it works out.