Far as lipo concerned - same deal - any 2S (7.4v nominal) that will fit. Lipos are usually described with w x l x h measurement. You should know what size you have currently (can measure it) look for something very close to same size physically. Lipos come in various mah capacities and as capacity increase so does physical size.

It will be pretty obvious what your lipo possibilities are once you know the dimensions of the space available for the batt. Go with the highest capacity you can fit in it. The other concern is a low voltage cutoff for a lipo if the esc doesn't have one already. An lvc protests the lipo from being overdischarged and possibly damaged or ruined.