I see one major problem. If using a 2 Cell Lipo, you will have less power (voltage) than the 8Cell Ni-Cd. Although the 15C Kokam packs are great, you won't be able to pull much amperage from them on a stock 400 brushed motor. I don't know what kind of motor you are planning to use or what your budget is. I'll give you two scenarios.

1. Use a 400 Brushed motor/Speed Controller with an 8 Cell Ni-Cd pack and a normal Ni-Cd charger. Most affordable.

2. Use a Brushless 400 class motor/Speed control with a 3 Cell Lipo and a specialized charger like the Triton or the Kokam 402/502.

Here's the reasoning...A three cell Lipo (11.1) will burn up a brushed motor pretty quick, maybe even the first flight. Remember, it was designed for 9.6v. A 2Cell Lipo only has 7.4v. This would make it fly even worse than the 8 cell ni-cd. Also, spending a lot of money for a lipo battery AND a charger is a significant investment, one I feel is wasted without also going to a brushless motor.

I finally took the brushless plunge a while ago on a plane similar in size to the Tiger 400 you are considering with good results. Hopefully some others will chime in with some affordable motor/ESC choices. Mine was on the expensive side. I can share my setup if you wish, but first describe what you want from your plane and what kind of budget you have. This will help all of us help you make the best decisions.