the cvr is a side exhaust motor while the tz is a rear exhaust motor so if you go with that one you will need a new header. with the cvr you can use your stock header and save some money here are some specs on the two engine that I pulled off of tower O.S 18 TZ Practical RPM: 3,000-34,000 Output: 1.8ps @ 29,000 RPM. O.S 18 CVR Practical RPM: 3000-32,000 Power Output: 1.35 PS/28,000 RPM. if I remeber correctly I think That you stock motor has around 0.7 HP so the cvr is almost double but don't quote me on that.
Here ivs a vid of my firestorm with the cvr. the quality is real crappy but it will show you the kind of power you can expect. I am also running rich in the video as it is still somewhat in the breakin proccess.
http://s129.photobucket.com/albums/p...vidpics003.flv