I’m not sure I believe those gage readings…But, areas 5&6 are within normal range…Try taking one more reading, right on the aluminum ID core plug located on the outlet flow from the powerhead. That engine doesn’t look like it has seen salt water but who knows…The paint is all off the block, so may have overheated at some point. I think you will be OK if you just replace the impeller using an OEM piece. But, have a close look at the aluminum water pump housing and SS plate, these items should be replaced if badly grooved or pitted.
This is a special engine because it is a folder complete with its case. So, you may want to consider pulling the exhaust cover and head at some point, the passages are small and get partially/plugged easily especially in salt water. I would probably pull the powerhead to check the rubber water tube grommet also. Again, I am only saying this because I would want to preserve this special engine, not because I think there is a cooling issue at this time…
