I would try racing a stock one before you go through the trouble, they are probably pretty consistent in stock form. I do not think the transmission would be the reason behind it if it wasn't. Modern engines will pull timing and add and subtract fuel if there is wide swings in intake air or coolant temp. If you can keep those consistent I imagine the time slips would be pretty close. I know a Local guy with a hellcat challenger and when it was stock I saw him run several 10.87 and 10.88 passes in a row.

I would love to have a 1320 Challenger, I would probably bracket race every weekend I could because it would be a simple drive to the track and get in the lanes operation.