Which Mopar Chrome box are you using? The early race chrome box with the blue heat sink or the later chrome one sold over the counter from any Mopar car dealership?

I'm using the later style one...it has a standard looking black heat sink on it, MP part# P4120534.

ET and speed from your OP aren't that far off ( that Wallace calculator is - happy ) from what you have. What are your 60 ft times? 38* total might be a little aggressive for your set up. Might try 35 - 36 total. Nothing wrong with the TQ. Plenty of carb ( even the small block version, which you are using ) if it is set up correctly. Are you running through the full exhaust, or open headers? High 12's, 103 - 4 would be the max you could expect with your present set up tweeked as best you could IMO. Then again, you have aerodynamics working for you .

Happy as in it predicts a higher mph than it should for a given HP or more HP for a given MPH?

When I used it ( no matter how I inputted the info ) it always made my actual #'s ( ET & MPH )look bad. MPH was always higher than I would/could run. I have a Moroso power speed calculator that is a little happy also.