Ok, first of all welcome!
*Disclaimer, the following is what I have come to understand and may not always be 100% accurate to your case*
1. Is it a Barefoot Skier? I own an 86 Barefoot Advance. I have been told that the only real difference in the Barefoot and the standard American Skier model is the engine and horespower rating. Please advance to question 2........

2. Engine is a 350.... Standard engines for marine use at this point in time were "Fords" 302s or 351's. If your block is a GM based marine engine that was original to the boat then there is a great chance you have a Barefoot. The GM based plants were almost always rated at higher horsepower than the Ford base plants in that day and age.
3. Cam, Cam, Cam....... at this point I am almost in the same boat as you (pun intended). I built my engine during my overhaul. I dont know if something went wrong with the build or if a part was bad from the factory, regardless I threw a rod..... Not good. I am in the process now of purchasing a GM performance crate engine. I cant use the stock cam so I had to do some hunting of my own. As a suggestion I would reccomend looking at comp cams Xtreme Marine series of cams. The cam I am ordering is a roller cam so the part number will do you no good, but if you contact Comp cams directly they will take your information and suggest the best cam for your application.
4. Oil pan. The only difference I could tell in my oil pan from a car or truck pan is the capacity. My pan holds 6 quarts of oil where a stock pan holds 5. There may be other differences, but if there are I dont know them. In fact my pan will fit your block but will not fit my new block (Im going roller block) so if you want a stock pan I may just be able to help you out in the near future. Get with me. Interestingly enough I powdercoat on the side and could make it the color of your choice before I sent it to you if you choose to go that route. You would need to be sure the dip stick tube is on the same side as mine as that usually was the only difference in the blocks back in the day as far as mounting them.
5. Speedo's, if one is leaking water from behind Id say its almost certain that your pitot tube has either come off the barb it is supposed to fit on on the back of the speedo or it has a crack or split in it. Water coming in is because of a hole in the hose either being open ended because it fell off or a wear point where the tube actually failed.
Also, your trim rings...... well Im not going to use the word impossible, but they are damn near impossible to find. Your best bet is ebay or a bone yard. They dont make them anymore and parts are slim leaning way toward none.
6. If it was me and I was building my engine (which I did) I would just replace the clock meter (which I did). Thats just my opinion. The face is almost certainly plastic and I dont know any way you can get it off to clean it up to make it look good. Not to say it cant be done.
7. I have no idea about your switches. That would be best for Ron or Dan to help you with I think.
If anyone sees anything I missed or that is wrong please speak up, Im just trying to help out here

I have given the most accurate information according to my recollection.
