That piece looks like the bracket that holds a shifter cable for a remote control. I believe that motor uses friction to hold it up. If it doesn't give us a pic between the brackets with the motor up. Might be a bracket missing or broken.
Which 150 do you have? I am going to guess it's a looper. Check for warped float bowls especially if they are plastic. Check the mounting surface of the carb for being warped.
Take the block to the machinist They will tell you what size piston you need. You don't order pistons off of guess work. Whoever bores the block will tell you what you need.
I will be the bearer of bad news for you. Your motor was obsolete pretty much within 5 yrs of being built. You need to find the software and correct cables for a first Gen Ficht. Parts availability is pretty much non existent. Good luck even finding a Mechanic to look at it. When BRP bought OMC...
Pull a 63 and 64 Evinrude apart and tell me the differences? My 1958 Scott 60 hp has the exact same bearings/block as my 68 McCuolloch 75 hp. Why is the McCulloch capable of 100-1 and the Scott is 40-1. It is because of the oil not the Metullargy.
Easiest way to build those pumps, is put 2 screws in a vice long enough to go through the unthreaded part. Build the pump on those 2 screws and stack it like a sandwich.
I think the takeaway from this is to know what you are taking apart. Don't just jump willy nilly into it. A lot of those pumps get rebuilt just need to be aware of what's in it. Google has many parts breakdowns for those pumps.
Your oil looks fine. Use 80w 90 marine lube for the lower unit. Use hand impact to get the lower screw out if it is to tight. Maybe replace the screw while it is out.
