Trope,
if the one from the Alpha fits and hasn't been compromised by the crash, by all means use it. Wrap it in foam as pictured and use enough so it can't move around. The center of the tank should align with the approximate center of the carb for your side mounted application.

The long tubes included with the new tank are the parts that pass through the rubber fuel stopper. One is used for the tank vent and is bent toward the top of the tank on the inside. The other is generally trimmed shorter and a piece of fuel line with a clunk is attached which will reach to the far end of the tank.
The vent line attaches to the muffler pressure port and the other to the carb inlet nipple.