ORIGINAL: CEN Racing
You can use up to .18 / 3.0 size engine in the fun factors without modification. Anything beyond that, you will need .21 conversion kit.
according to cen it will go straight in
the os18cvr-x is the best side exhaust .18 out there, but the Team Infinity is hard to ignore at that price, unless they are a nasty motor of course - have a search or ask around for Infinity owners' comments, see if they are any good before buying.