no idea on a cheap TZ - is there such a thing? nice motor, stock up on diff cups or do the mod which is on here somewhere. have u considered the 18cvr-x? its a big jump from the nt16, and at $90 odd, its a steal.

there are some .21 engine mounts (part number CT040) that should let the 25 drop right in - they work with an SH.28 and some .21s for sure with a touch of pinion/clutch bell shimming, so they should be ok for you too, i think. good luck in finding the mounts tho!

quite a few funfactors have had a .21+ installed it seems, and all the owners have accounts of ridiculous speeds etc! it is fun mate, just expect to break it a lot without further mods.