I did not install the MSD myself, but I did " watch " the procedure. From selecting the springs and stop busings, removing the old distributor and installing the MSD was approx 1/2 hour by an experienced mechanic. Time includes answering my questions
Regarding the timing options. The MSD includes three sets of advance springs and four stop bushings. The springs determine the rate of the advance, how fast the timing advances. The stop bushings limit how far the weights can travel, stopping the advance. In addition to the initial or base timing. That said, it sure did make a difference and allows for a variety of settings based upon driving needs.
Also replaced the spark plug wires with MSD 31349, $72 from Summit
www.msdignition.com