What length to make new shrouds?

[Brion Toss]

Hello,
If you choose the right diameter, use HSR or Colligo's rope, and pretension accurately, as per John Franta's excellent protocol, then I would go for 3/4" extension. This will give you enough takeup length for many years of incremental creep.
Have some extra toggles or lashing material handy when you step; the rope tends to shrink up on the way to the boat, and you might likely have to work the constructional set out before you can remove the extra bits.
Fair leads,
Brion Toss