After my previous answer, I browsed through the internet and found this site,
http://www.oconnorclassics.com/techtalk_neg.php
which seems to cover everything that might need adjusting. I do not remember doing everything it describes when I rewired my 62 MGA, but that was 19 years ago, and I may have jusrt been lucky about the ignition coil wiring. Check the above site for some well-worded instructions about converting to negative ground.