I'll have to double check. I didn't install the tank so I still have it in it's plastic cover... I'll post this later.

You can indeed put a larger tank in there.

To be able to fit larger batteries I used a coping saw to open up the former a bit, which normally supports the mid-rear part of the tank.

You could simply get rid of it too, as the fuselage is strong in that area... the people who are putting in Jet Engines on the larger models do this all the time and they seem to have no problems.

You could practically double ( or more ) the size of the included tank.

Re: Pipe

On my .52 I ended up routing the exhaust right thru the wing. This has worked well.

I suppose you could do the same with a pipe too.