I don't know savages at all, but if the new tank is taller than the old one, it stands to reason that you would have gravity working for you as well as muffler pressure because there is effectively more fuel above the pickup going to the carb which increases the pressure at the pickup. This could cause problems if too much of the tank is above the carb. I doubt it would be too much of a big deal on a monster truck though.

As for the shorter fuel lines - longer fuel lines usually work within reason, however the longer they are the harder it will get for the engine to pull fuel. For best fuel draw and needle setting ability, you want the tank as close to the engine and have the fuel and pressure lines as short as possible. I run LST2 trucks and run the fuel and pressure lines "just" long enough. Plenty of time to run and flip it back over and clear the air bubble.

Hope that sheds a little light on the subject?