BTW....Welcome to i-boats!
Well; of course anything can be fixed. I was in the same situation as you a few years ago. A friend had given me a free boat with Merc 850 on it. The wiring was so bad that I would not chance even hooking a battery up to it. I wanted to check the compression to see what I had; so in order to save money I just went ahead and re-wired it one wire at a time. That way I was able to get it running and further evaluate its over-all condition before spending $$$ on the genuine harness.
It's do-able that way...but you might find that the condition of the wires is so bad that it's difficult to solder on to them.
CDI makes aftermarket ignition components...Switchboxes, Stators, Triggers...They seem to get a good rap here and I have used their products.
Their products are available thru i-boats and they have their own website:
http://www.cdielectronics.com/Products.aspx?Criteria=4
If you want further help, please post your engine's serial number. That way you can zero in on all the various parts that you might need.
Your engine sounds like it would certainly be worth re-viving. You probably won't need to invest much to bring it back.
I'd be interested in following your progress....
Chuck