Hey, I have an older Revo 2.5 with a 3.3 in it. The engine is starting to get a little tired, and was a little underpowered to begin with. I would like to drop in a big block, but I have heard that only a few are compatible. I really do not want to pay nearly $300 for a .21TM when I can get an axial 21 or 28 for a fraction of that, but will they fit? Someone was telling me I would need an extended chassis in addition to the conversion kit. Is this true?