Just installed the Pertronix MR LS1 on my 1977 Spider. Idle was fine; cruise was fine; acceleration was awful -- spit, cough, jerk, backfire.
The screws included with the set to attach the base plate to the distributor-points plate were too long. They protruded so far through the points plate the advance weight pins hit them. Ground down the screws and it runs fine in all modes.
Be aware.