I made a 49.5" minred. 26oz and the balance point is almost exactly 18" from the end of the pommel.
I used .602 kitespar from Warlord sports and a couple of duratubes to make an Omni greatsword.
To drastically weight the pommel I used tent spikes/large nails. You can buy them at Home Depot. They are huge 6+" nails that are more like spikes.
I wrapped duck tape around it to secure them into the hollow core then built my pommel overtop of them. The head of the nail will stop it from sliding down and your pommel + tape will stop it from coming out.
Kitespar may not be your thing. It works great for me, but I know some who say they break it all the time. But other than being a solid core it meets all your other requirements. And I really enjoy the low balance point. Makes it really fast and maneuverable compared to most other reds I have tried.
Here is the link to the warlord sports weapon I based it on.
http://www.warlordsports.com/omniblade-greatswordHope that helps.