You will, I bet, hear a lot of advice regarding which guns to take. I'd ask first; What guns do you have, and what guns do you shoot well? For most plains game any of the classic deer calibers ( 30-06, 270, 7x57, 280, 7mag) will work well. Eland, on the other hand, is as big as a Cape Buffalo, but not as mean. 375 H&H is a good option for eland. The key question is what gun do you shoot well? a hit with a 270 is much better than a miss with a 470 Nitro Express. Many people fall in love with the mystique of Africa and buy a big bore dangerous game rifle only to discover that they don't shoot it well. Big calibers tend to recoil a lot. I'd suggest a two gun battery consisting of your usual deer rifle for everything except the Eland and a 375 H&H for the Eland. Or take a 375 and a shotgun if the bird hunting is good.
On my first African trip I took a 30-06 and a 375H&H, on my second I took a 375 H&H. I took Cape Buffalo, Tessebe, Kudu, and Hyena with the 375. With the 30-06, Kudu, tessebe, impala, lechewe, and warthog were taken. Absent the Buffalo, the 30-06 would have been perfectly adequate.
I would suggest that, in addition to this site, you check out Accuratereloading.com. There is an active forum dedicated to African hunting.