Rolf,

I know a chap who built a Marmian set of A class (similar to AHPC MK3)back in 89 fitted with an Alspar aluminium mast with an all up sailing weight of 74kg. 1kg under the current min for the class.

The boat is still being sailed.

This chap had built before and knew what he was doing.
Probably not a project for the first timer unless there were very exact contruction instructions including exact quantities and weights for all materials. (BTW:- when selecting cedar I have measured variations in weight of 50% and found the lighter the colour of the cedar the lighter it weighs.)

When you compare the modern shape the Marmian has greater surface area so from that point, in theory, you should be able to build todays shape even lighter. The use of carbon striker straps, (if you choose to have one) carbon beams that can be glued in etc should further help reduce weight. (Beam bolts and striker strap are heavyier than you'd think.)
The only problem is coming up with a modern shaped design that has light enough building techniques.
So I think it would be possible, but there is a big gap between the possible and the actual.
Someone would have to committ themselve to doing and prototyping a design to make it a reality.

If anyone gives it a go I'd be interested to hear how it turns out for them.

Just the way I see it.
Regards,
Phill