RE: fantom .18?
First it is TRX 2.5 not .25 - The TRX 2.5 is a .15 size engine. The Fantom .18 has loads more power than both. The .18 physicly will fit fine, but all the steps in setting it up and getting it to work is up to you or getting help from someone who physically can see it.
I would go with the Fantom .18 myself. I bought one for my TMaxx but have not finish the run in proceedure yet.
Cheers, Keith H
PS - if you ask something in a post a post, please be patient and dont email everyone the same question.