Hi Steven,
AFAIK there is no heron specific info on this - but prehaps a member with experience will chip in. I think there was a rule change a few years back which allows the case to extend forward to the king post for extra rigidity.
Dinghy Sailing Magazine had an aricle in April 2004 on this (just after I attempted my own case repair (badly!!)

) DSMs was on an enterprise but the essence is the same.
The steps they followed were:
- Strip the varnish/paint back to bare wood. They show a heat gun being used for this. And I'd say they go about 1.5" above the join. Curiously in the photos the c-board case is held in place with a wooden bead (mine is on the heron although the bead is very thin). The curious bit is that the seam they repaired was the cb case to bead seam and not the bead to floor seam... I think all of mine leak!
- Sand the area to create a smooth area & brush clean +/- hoover
- Mask off the area above and below the seam I'd say they left about 1cm unmasked either side of the seam.
- They used SP320 Epoxy (Any boat epoxy will do!) Mixed as per manufacturer instructions.
- They then used micro balloons mixed into the epoxy... find all these filling substrates confusing: When I repaired mine I used Glass Bubbles which are pathetic. Micro Balloons are suposed to be better at making 'cosmetic fillets' but personally I'd have though micro fibres would have been better. Anyway the general advice is to add these to the epoxy to get a penut butter consistency. Not eating penut butter that gives me problems!
- The idea is that the filler epoxy is thick enough not to run away (it should be spatula'd onto the seam and smoothed to a concave) - but should be runny enough to just seep into the crack you are filling. The manufacturers usually give a suggested mixing quantity - but to confuse me they quote a % weight. I don't have scales in the garage and Nicky doesn't seem to think I should use the kicthen ones
- They then left it to set (I'd have left it an hour, then removed the masking tape
) But they don't remove the masking tape until the stuff is rock solid!
- Sand any rough bits and varnish to make it and the wood you stripped water tight... and then go sailing!
Hope that helps.