If you have the money to spend I would recommend spending it and doing the Tekno conversion. I wasn't aware of the Tekno conversion back when I bought my Losi conversion kit or I very well might have gone that route myself.
Motors do have standard sizes and your typical 1/8 scale motor (670 can size) is 40mm wide but if you include the small fins that most motors have on them they are right at 42mm. So ya in terms of diameter any regular 1/8 scale motor will work with that conversion kit. The one thing that isnt always standard is the length of the motors. Make sure the conversion kit doesn't have any length restrictions and you are good to go. If it does have length restrictions then just make sure the 1900kv will fit.
To answer the question about whether to use the 1900kv or not I would say yes definitely use the 1900kv if you want to race on the track. It has the right amount of acceleration and top speed that is apporiate for a track setting. It will still be plenty fast off the track too plus if you want a little more speed out of it you can throw a 5S pack in it and get some more top end. Watch motor temps if you go from using a 4S to 5S lipo though. more voltage will mean more heat if you are using the same pinion.
To expand on Mudslinger answer to your previous question let me throw in this. The voltage of the lipo directly corresponds to the RPM of the motor. For example if you have a 1900kv motor that means for every volt of electricity you put into the motor the motor will spin 1900 RPMs so a 1900kv motor on 4S would spin at approx. 28,120 RPMs. 4S lipo = 14.8V. 3.7V per cell times 4 cells. So, 14.8V X 1900kvA = 28,120 RPMs. 1900kv on 6S would be approx. 42,180kv. It should be noted here that the Telin 1900kv is NOT compatible with a 6S lipo I just used that as an example. The max cell count lipo you can use on a Tekin 1900kv is 5S. Most of this stuff is covered in my videos though so keep watching
As for the C ratings of the batteries, the C rating works in combination with the mAh value of the pack to determine the maximum amps the pack can safely output at a continuous rate. Example a 40C 5000mah pack can put out 200A continuously without damaging the lipo. 5000mAh/1000 = 5A. 40c X 5A = 200A. 25C lipos are to low to use in most 1/8 scale kits IMO. A 25C 5000mAh lipo only outputs up to 125A.
5000mAh pack are among the most common but you can use higher mAh packs for longer run times as long as the pack will fit in your tray. Always make sure the lipos dimensions fit your tray before buying a lipo even if its a 5000mAh pack. Now you can also go a little lower on C rating if you have a higher mAh value pack. for example if you had a 6800mAh 30C pack it can put out up to 204A continuous so its right on par with a 5000mAh 40C lipo in terms of the amperage output they can sustain.
Let me know if you have any other questions and finish watching the vids cuz they go into even greater detail on most of these topics.
