If you can get the scanID, one of the items available in the datastream, then I may be able to identify the calibration.

You say you are building a 350, but what does that mean? Rebuilding to stock, or are you changing cam, pistons, heads, etc? Changes to airflow require changes to tuning.

The older C3 ecms like the 8746 and 7747 contain most of the program to run the computer on a different chip than the eprom with the tuning data. The programs are different between the two computers so you cannot directly install a 7747 $42 calibration in an 8746 ecm and have it work properly.

With your experience from the last time the tuning process might not take so long.