You may want to check out the Carbon Tech Safari's. It is 15.5 GPI and with brass inserts and/or heavy broadheads I am sure you can get the weight you need.

http://www.carbontecharrows.com/Hunting/hunting_master_detail.php?ModelNumber=S500S

Your best bet IMO is going to be using a Grizzly Stick, specifically made for game like cape buffs. Really heavy, durable, come with everything you would need like inserts and things. www.alaskabowhunting.com is who sells them. With their inserts and a 225gr broadhead, easy to get up to 900+ grains. Definitely worth a look.

Whatever happened to the NAP African head at 260 grains?

PSE also makes the black mamba which includes 10.5 gpi weight tubes.They come with stainless steel inserts and collars. I set some up for a customer a few weeks ago that was going to africa and it seems like they weighed about 600ish grains with out a broadhead. With a 200 - 220grain broadhead you should be able to easily reach 800 grains total weight.

http://pse-archery.com/prod.php?k=56063&sk=56063&u=RXB#

You could also use solid brass inserts, steel adapters and a 190 grain grizzly broadhead. That would give you about 415 grains up front.

THANKS FOR ALL THE INFO