Based on the original manual, an "I" of 42.0 and a "J" of 12.0, so by formula, the max theoretical length of the forestay is 43.68ft. There's really no such thing as a standard furler, every installation can vary, you'll have to deduct for the drum height above deck and the swivel at the top.
If you know the brand of furler, there should be published standard deduction, usually around 14 inches or so, unless you have extensions putting the drum up higher off the deck.
The best way of course is to run a tape measure up the halyard, gently pull it to the top of the hoist and measure to the tack on the drum.
Happy weekend.
dave