Ok, lets forget about what you have done and try this.

Check the media unit FADE and BALANCE setting to make sure they are centered

Look at the suspect amp's settings to see if his has mode switch labeled something like 2CH and 4CH. If its 4CH move it to 2CH - Do the bow speakers work Y or N

Y = See yah!

N = swap the RCA from 1/2 to 3/4 and from 3/4 to 1/2 - working? Y or N

Y See yah

N = remove RCA from the working "working" amp and plug them into the suspect amp's 1/2 ports - bow speakers working Y or N

Y = issue with the four RCA feeding the suspect amp. They could be Y'd just behind amp wall and one Y is bad

N - Looking like an amp. However, I dont suspect amp as somehow some way you've made the bow speakers work and I cant make sense of it.  

FWIW my detail guy (40 years experience) who does a lot of ceramic coating advised me to stick with buffing and waxing vs ceramic coatings on fiberglass boats.  He said that he has found because of water spotting, river scum etc. ceramic coating still requires buffing and waxing to keep it nice, and it doesn’t last as long on fiberglass as it does on metal painted surfaces.  He basically did the math and said $3k+ for ceramic coatings pays for 6+ full boat details with buff and wax inside and out.  The only way the ceramic coat boat looks as nice as the boat that got 6 details in 3 years is if you still did the detailing on the ceramic coated boat, and even then it would be hard to tell the difference.  

Says 89 or 93 for LS1.  I would run non-eth 89/92/93, whichever was obtainable.  I’m not sure if the manuals were addressing eth vs non-eth back in those days but I would just assume those engines are designed for non-eth fuel.  

No idea about the custom ski ropes but it sounds interesting and I’m sure there are niche suppliers for it similar to fishing rod blanks.  You’ll probably find that the reasonably priced stuff available is suitable for your needs. 

As far as you fuel question goes, the specifications section is likely the best place to find your answer.  🍻 

I’d try asking on Ball of Spray. I don’t see much in the way of individuals custom making their own handles.  But you can buy reasonable handles from S-Lines and Masterline as well.