Bvining,
You can build ply A class's at min weight from ply.
I know 3 guys who did it in around 1989 with alunimium masts.
I'm told when weighed they were 74kgs rigged.
I believe this to be a legit weight because they sailed in the worlds either that year of the following and they had to be weighed.

Now this is an older style of hull which has more surface area too.
You have to be good, very good, but it can be done.

BTW:- In recent years I've seen two of them still sailing.
Don't know where the third is but I think it was sold overseas.

Regards,
Phill