I would suggest renting not buying a second body. A full frame body has far superior IQ to an APS-C and this would be the way to go. Check out lensrentals.com or another rental company (assuming you are in the US) for a 6D. The 500mm is an overkill (8.5 lb lens)- I would suggest the 70-200 2.8 II lens with a 1.4 and 2.0 TC instead. This with the 100-400 along with an APS-C and full frame bodies would be close to an ideal set-up without spending much more.

Also I recommend the following book specifically for an photographer going to Tanzania.

http://www.amazon.com/Wildlife-Photography-Equipment-Techniques-Workflow/dp/1933952563/ref=sr_1_4?ie=UTF8&qid=1358995081&sr=8-4&keywords=wildlife+photography

Most quality outfitters will include sandbags. If not, carry one- 18lbs is about the right size (the weight after you fill with sand, rice or beans on location)
http://www.bhphotovideo.com/c/product/420376-REG/Impact_SBE_18B_Empty_Saddle_Sandbag.html

A tripod is very useful, no way around that. Get a very lightweight carbon fiber one rated for 5 lbs with the set-up above (will NOT work with the 500mm)

Well, you need a wide angle 17-85mm, is perfect. And then a zoom such as the 100-400. And you need two bodies, put the 17-85 on one and the 100-400 on the other. You then reach over and pick up the one you need, no lens swapping. Forget the 500 F4 unless you are very experienced wildlife photography and truly know when and how to use it. Whether the bodies are so called FF or APS-C really makes little difference. How you set up the camera and your Photoshop skills are more important.

UV filters not needed on digital lenses. Unless under extreme environmental circumstances. If you simply have to have them, get the best, B+W. Most important is the lens hood.

More important than any of the above for photography is being allowed to go (drive) off road. Off road to best position the subject, the light, and yourself. Some places in TZ you can, e.g. Ndutu area, some you can not, e.g. Serengeti, nor Ngronogoro Crater. Tarangire NP I don't know.

Sand bags work great for pop-top vehicles. Tripods only if you plan a -lot- of sunrise-sunset photos. You can get nice ones with the bean bag. I use flash only for building interior shots. Don't care for flash on wildlife. The 60D has pop up flash so it's probably good enough.

regards - tom

Check with your tour operator to find out if sandbags are included in the vehicle. When I went to Tanzania they were - and they were large heavy ones that were perfect for steadying the camera.

While UV filters aren't "needed" on digital lenses, they can certainly save your lens from scratches or hits. You'll be rough, dusty conditions and a filter is cheaper to replace than a lens.

When we ran into very dusty conditions in TZ, not often, and caused by vehicle(s) ahead, we put our whole camera in a (bed) pillow case. Dust/dirt -inside- the camera/lens mechanisms is not good. A dusty front lens element can be easily cleaned using proper procedure - blow, brush, lens cleaner fluid on a fresh unused lens tissue. Throw away those micro-fiber multi use cleaning cloths (for lens). AKRI above mentions Lensrentals, here is how they clean 250-500 lenses per day.
http://www.lensrentals.com/blog/2011/05/the-lensrentals-lens-cleaning-methods

regards - tom

Here's another lens topic from Lensrentals. "How to Test a Lens".
So you buy a new lens, it should be perfect, it's new, right?
Probably, but maybe not, here's how you can check over your new lens -
http://www.lensrentals.com/blog/2010/11/how-to-test-a-lens

Over my (70) years I've purchased few lenses/cameras, only around 10-15. And there was only one new lens, Minolta 100mm close-up, that disappointed me. I sent it in to Minolta and they repaired it saying an element was off-center. It was then after a great lens.

regards - tom

My last Trip New Adventure Safaris did all for us, ask them.
www.newadventuresafari.com

As an alternative to sandbags, in both Kenya and South Africa, I used supermarket bags of split peas or lentils. Two pound bags work great (or stuff a couple of one pound bags in an old gym sock). Buy them at home or in a local market when you arrive. Give them to your guide or a local on your way out of the country.