The trim tab is non existent but i believe it's supposed to be right above the prop. I point to it first thing in the video. I assume by fasteners you mean bolts? I point those out in the video too. I say loosened but I've taken them off... just put them back on a bit so I don't lose them...
I got this boat last year. The guy that sold it to me said the motor (1978(ish) Mercury 50) runs good but needs a new impeller. He had tried to get the lower end off to change the impeller but couldn't. I took on the challenge but I am also stumped.
I'm hoping someone on here knows the trick...