I have a Nacra F18, located in Truckee. Would love to get some group sailing in this summer!

Looks good. Be sure to check those 40+ year old hulls for soft spots.

Also, something appears to be rigged incorrectly with your main halyard. The portion of the line that comes back down the mast should be inside the mast, coming down the sail track - yours looks like it is routed outside of the mast.

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From my limited experience, the boat appears in very good shape for a 1981. I was told it was always covered and doesn't show any signs of soft spots.
Yes the main halyard was outside and also inside the mast. It's one continuous rope loop running up inside the mast, over the upper sheave, down outside the mast to the aussie ring, around the lower sheave and back inside the mast. Half the line stays inside the mast and half stays outside. My main halyard line is slightly wider than the luff track so its difficult to squeeze inside (I do not have a comptip). Do I disconnect the continuous rope loop once I attach the main sail? I tried re-reading the manual but I wasn't sure.

That would be a lot of fun. Where have you sailed around the Truckee area? Anywhere you recommend?

I sail mostly Donner and Stampede. Would love to sail Tahoe more but it's so expensive!

Nope, nope, nope. It sounds like you have it backwards. The tail end of the main halyard runs inside the mast and is used to hoist the main sail. At the bottom of the mast is a sheave around which the tail end of the main halyard runs. Connect the main sail headboard to the halyard ring, then insert the main luff into the luff track, and hoist by pulling the halyard from the tail end at the bottom of the mast. Once the main is hooked at the top, coil the tail end and stuff it into a tramp pocket (if you have one).

The halyard is not a continuous loop.