If this were me and I wanted to do the least amount of work, the 1st thing I would do is after the engine was together, is take it to an engine dyno that can run MY stuff IE headers. Then I would fill out the form and attach the dyno sheet with the corrected and uncorrected numbers. Since I now have the HP that the engine makes and at what RPM, along with the weight of the car (you do know how much it weights?). I can tell what MPH it should run. With this info and knowing what tire size I have I can select a rear gear. I would send ALL the info to the converter guy and do a one shot one kill on the converter.

What I wouldn’t do is let the converter guy give his best guess at what the engine makes and me guess at the correct gear and weight of the car. That means I am going to spend ½ the summer removing and replacing parts instead of racing. Been there done that, never again.