Take a piece of cord, attach it to to your spinnaker halyard and raise it to top. Measure from the bow fitting and subtract 2 feet. That will give you a luff measurement.
In theory the rest should follow, as the dimensions ought to be similar. Some Cruising Chutes are high cut to the clew to allow better visibility, and will be cut much fuller than your Genoa. At a guess you are looking at about 165% in Genoa terms. Total square area will be as much as 85% of the equivalent Spinnaker size for your boat.
-------------------- Come on over to the East Coast Forum . You meet a nicer forumite there.