I have the engine out of my 67 w/289 and the previous owner put in an aftermarket torque converter. I’m not sure its details but he was going more racey and i want a nice daily cruiser. I have the factory one, should i replace the new one. I am assuming the old one is fine, i’m not sure what exact difference it will make? It shifted fine but a little jerky when downshifting. Thanks 
IF it was shifting fine then it’s probably a good match to your cam…you really need to match the cam to the TC to get the benefits of any mods. In reality a solid shifting trans will “jerk”. Stock trans’ have a bit of a slip factor to make them seem smoother - but it also wears the clutches a bit more. Sounds like you had a decent setup then…