You can get a lockup converter (23 spline) with the lock up feature eliminated. I think those are still somewhat reasonable in price. Ultimately, the converter clutch depends on what you are doing. You would not want to try and lock the converter under heavy throttle, it's going to slip. If adding one of these transmissions behind a big block using the JW ultrabell, you are limited to a 10" converter (due to the ID of the bellhousing). Getting a 10" lockup converter is expensive, say $600 and up. If you are putting one behind a small block, there might be more options but those would probably be limited to a larger diameter (12") converter. The V10 and diesel converters (which are gigantic 13") have options for multiple clutches and maybe one of those setups could be adapted for a 12". The unknown would be if the stack height of the converter would require a spacer between the trans and engine to fit it all in there. Ultimate (I think) Converter could build a 10" lockup for me but they required a 1/4" spacer. Since I already had everything else built in the car, adding that spacer would have made me have to go back and redo the exhaust, crossmember and trans mount at least. A place up in Redding, CA. built mine at the stock assembly height (Spec Rite Converters) but it was expensive. I'm pretty happy with mine so far. Again, you wouldnt want to try and lock the converter under heavy throttle and you probably wouldn't leave the converter locked if you were to floor it. Other than that, a converter is a converter. You can build something as crazy as you want (billet front end, billet stator, steel stator, mechanical diode and so on) depending on how much money you want to throw at it. If it's good enough for a cummins diesel with 500 ft lbs of torque in a 5500 lb truck stock, it should be ok for a 3500lb car with more power.
