There seem to be many who don't think a plane flys well unless it can go straight up. Your BLT will fly, but like a trainer. I didn't fly my BLT stock, but with components close to stock. I decided to fly my BLT with GWS motors and gearboxes because GWS has a bunch of information on their power systems on their website.

As far as lipo's, nothing is impossible. I don't have my BLT to test this theory, but I would suspect that getting the CG right would be a challenge. If I were building one now, I'd consider using a light outrunner, rated at about 100 watts, and put a small lipo on top, in front of the wing pylon.

But I definitely wouldn't use a lipo on a BLT until you've got more experience. The nimh cells (you should use nimh, not nicad cells) will survive the crashes better. and the BLT doesn't crash well. I learned the art of rebuilding.... Other than some punctured covering, the wing never suffered any damage. My favorite part of the plane!

I did't think the plane was heavy. Go easy on the glue. Use a lighter covering on the wing and tail to make it even lighter.

You can without doubt use the old ESC if you are using a 2S (7.4V) lipo IF you are careful with the voltage cutoff. ESC's cut power to the motor before the battery goes dead so you still have power to the electronics. Problem is, Lipos don't like being overdrained, and if the ESC isn't designed to run with lipos, there is a danger of overdraining them. Once you get experienced, you'll likely never run your batteries 'dead' but until you get experience, you don't know how to calculate and get a sense for this.

An older ESC could burn up if used with a 11.1V Lipo. Check the specs, get a new ESC, or ask how to calculate flight times. But basically, the 650 mAh battery will give you about 10 - 12 minutes of flight. If that is the case, I'd only use an 800 mAh lipo for 12 minutes of the same kind of flying and then land.