You want to look at a Tornado for ideas as well Robbie Daniel pimped a P19 in Florida this way. IMO.. the Tornado chute proved a bit to much for the boat though in a blow.

Your basic problem is that you can't have the pole too low... or you will pull the bows together.

Harry in MD pimped his P19 out with a Tornado chute, tramped bag launched and stock jib. He used a Nacra 6.0 foil to protect the bows... Way to much crap on the boat... it's nose heavy and the spin is too low.

IMO... i would keep the existing bridle (safe for the bows).
have the jib recut with a clew plate for a self tacker or get a new one. Nacra sells the track and kit to rivet onto the front beam.
Use a piece of dynema for a spin bale and an F18 spinaker mid pole system. You probably can sheet the chute from the shroud... Or try using a car on the old jib track slider if the lead is not right.

Remember... the huge mx jib was to compete with the SA of the Hobie 20... Once you add the spin.... the jib is in the way. So... you want high aspect self tacking jib for max upwind performance.

IMO... The Tornado chute is a bit much on a P19.... The luff is a bit too long and so the pole is very low .. even with max mast rake.... and then you need a dolphin stiker on the pole to keep it in column and loaded. The F18 chute should be a good fit.

Lots of sailmakers can build a max area main. just remember you can't rake aft too much... because you have to sheet hard enough to close the leach without going block to block. This setting then sets your pole height... which then sets your spin luff length.

Work from the back of the boat foward.

have fun