thanks for the ideas Doug!
my cat has 4 stays supporting the mast; two to the front of the floats
and two to slightly behind midships. my current jib doesnt act as a
forestay, it has a wire luff and clips to a crossmember at the front of
the floats and then hoists with the jib halyard. does this change
things at all?

The self furler is a very close match at the luff and leach but quite a
bit bigger across the foot... should i have it re-cut or should i try
to move the tack further forward? being bigger it would probably afect
the ballance of the boat wouldnt it?