Hi Viking,
that's a bugger for sure. but is easily resolved with a longer mast extension.
i have been using kults since about 2001. they have all rigged on my 430 which is the suggested mast.
i use a 45cm extension set at 40cm with the 430 mast.
for me, being able to rig the 6.4 on a 430 mast is a great outcome.
hope this helps as you won't need to buy a new mast.