coil without ballst resistor?

Actually (my car is STILL apart) I used, as an experiment, the stock Mopar coil with GM HEI. It worked fine, and gives a hotter spark than with Mopar ECU. Be aware that some coils (according to internet wisdom) cannot be operated horizontally as the windings "will be out of the water". (Even though some coils WERE mounted horizontally "back when" including Ferds and some Mopars