You do have an encapsulated keel, that is how mine is on 9.2A (same hull). My surveyor said to make sure the keel is supported back and front when blocked (set down in the yard). I believe the bulk of the weight and structure is in the forward part of the keel. When the boat is out of the water you can tap on the keel and tell that the front is more solid than the back part.
I replaced my halyard (and all my lines up the mast) by doing basically what Gary said ... tied line (I used cheap green fishing net line) to old halyard with say 3 half-hitches spaced about 3" apart. Then wrapped the whole deal with electrical tape so it would feed smoother through the sheaves. Got old line down, tied off the fishing net line. When I bought new line, attached it to fishing net line in the same way w/ half hitches and tape, then fed through. Be careful, DON'T PULL TOO HARD when feeding the line or you might pull all the half-hitches off and then you have to climb the mast.
1980 S2 9.2A (30') in Anacortes, WA
Aux power 13hp Volvo MD7A