Hi Russell

It sounds like you are thinking of the Taipan, not the Mozzie.
It's basically the same construction technique in plywood, and yes they did go to a square top main. You should talk to the Taipan Association (or possibly AHPC) about plans. AHPC supply the masts and fittings as well.

If you are serious about wanting to "make it as modern as possible" then you should be building an F16 (not a one-design). The Blade plans are available for plywood construction, from Phil Brander.

Good luck.