One which may be an issue is the tachometer, and that's only if the gauge doesn't have a setting for the number of cylinders. Only other issue I can think of which may be an issue is the sensor size (if there is enough room to install)
Your new motor needs a 10 pin harness connector which has 9 wires in it. Pick up a 10 pin pig tail, cut the connector off yours
https://www.hardin-marine.com/p-13226-mercruiser-style-wiring-pigtail-mercury-plug-instrument-side-12.aspx
Need to wire according to the motor installed and not the helm
A 1976 used an ampmeter and not a voltmeter. Suggest wiring using current configurations
Have the manual for a 76 Merc but none show wire listing you have. All show
1-Black
2-Brown
3-Green
With compression that high there is liquid in the cylinder. Head is warped so gasket is not sealing or cylinder is cracked and water is leaking in.
When the motor diesels, that's when motor runs in reverse just before it dies and sucks in water. The water can bend rods and break things
The...
You need a real machine shop, that guy just has a sign up
If its not to far gone, find a machine shop that will turn it. Also have block cleaned to make sure there are no filings in the channels. Also look at the oil pump, may need replacing
The crank and rods are NLA, and I would not try to put an old crank/rods in a newer block
Unless you know what caused the second set of bearings to get eaten, I would look for the cause first before going further
Do you know?
There is no fuse on the wire and the neutral safety switch is inside the throttle control.
Look for 12V on the Yel/Red wire at the key when turned to start
With the Racor having a lot of crud, the first thing I would do is replace the secondary filter
https://www.mercruiserparts.com/bam/subassembly/31205/2673/170
The ECM adjust to keep idle within spec, but can only adjust so far. If one or more injectors are not getting the correct amount of fuel then there may not be enough room for the ECM to adjust.
There should be a code thrown and the MIL light would be illuminated. You didn't mention the light...
