Hola,
This is how I fix longboards.
A) First of all let two halves (partN(ose) and partT(ail)) dry for some hot days.
B) Clean edges of both halves from loose bits of foam and fibreglass. Test and clean till 2 parts fit.
C) With a handsaw, make two cuts on the foam,one each side of the stringer, from top to bottom. These cuts should be, at least, 200mm long and approx. 5mm wide. The same for both partN and partT.
D) Look for two wood panels (350mmX100mmX5mm). I usually find them in the dustbin of a near greengrocery’s (being part of the wood boxes for fruits).
E) Mix some lam resin+catalyser (hot) and paint both sides of each wood panel. Add some filler to the rest of the resin and pour it over the broken surface of one of the surfboard halves (partT).
D) Fit the wood panels into the slots made in partT, not flush to the deck, not flush to the bottom.
E) Hold partT vertical (between 2 chairs, for example) and fit slots of partN around the wood panels, which are waiting rising up from partT. Align rocker and apply pressure till resin sets (a hot mixing here is great help)
F) Sand wood panels flush to deck and bottom. Sand gloss and hotcoat between 100mm away from wood panels tips (100+350+100=550mm).
G) Glass with 2 pieces (500mm long) of 4oz. for bottom and 2 pieces (500mm long) of 4oz. on top.
H) Hotcoat till the end of sanded area. Sand and polish.
Once finished, wood panels should look like this (around the stringer instead of a finbox):
An example of a fixed longboard (by me) with this method: