Solent Stay

[benz]

Making sure the jib will fit before rigging up a whole setup doesn't seem too hard. Lash the tack to the deck, then run the head aloft with the jib halyard and see where it ends up. Choose a calm day.
I'd suggest tensioning the Dyneema forestay from the foredeck, if you have to go up there anyway, rather than leading aft--it'll only take a moment to pull it all tight, and there'll be one less line back there. I use cascading Antal rings for my running backstays, and they work fine.