Maybe you misread or misinterpreted how you were being dealt with. 99 percent of posters go away thanking everyone for giving them good free advice. It's easy in an online situation to take things the wrong way.
With that being said, let me list the things that are well known in the industry...
Clean it super good, sand and scuff up the existing paint, marine primer on all bare metal. Then numerous coats of desired marine paint. Clear coat.
Oh, I left our mask it.
Paint, 90 percent prep 10 percent paint.
Somehow I doubt the motor had 150 psi when it left the factory floor but maybe....a used motor should not test to 150. Something feels wrong with your test.
That being said, sounds like you have crud in your head. Remove head and check. Someone knew it had a problem and tried fixing it by...
50 to 1 will be 16 ounces per 6 gallons of gas not what was mentioned before.
Also, just like Racerone recommended, compression test. It will give you indications if you have internal damage
Pull this fitting off the block and start it up and see if water squirts out....I've scene them plug behind it.
Also, buy an IR gun and shoot the head and see if it's overheating.
When checking for spark and doing compression checks your coils need to be grounded otherwise you are putting extreme pressure on them.
I'm also assuming you have checked all grounds.
