A lot depends on the length of the spring that you are swapping out, and the thickness of the wire it was made from. If you use a very light spring it can allow the advance to come out very fast, but also if the spring was not meant to be used in a longer slot it will eventually stretch and cause other problems later on (I have a few that are permanently like a stretched slinky that did not last long at 5000 rpm in a 15L slot....).
If the spring loses tension by being over extended and the other spring doesn't help moderate the advance the pins can move to the ends of the governor and slap off the end of the slot allowing the spring to gain some tension back but causing the timing to wobble +/-4 degrees (seen this in the 11-13R governor using light springs meant for the 9R or shorter governor, it works better replacing the light spring only and using the normal 9R long loop spring to moderate the final advance and keep the final advance in check).
If you don't anticipate doing any racing or going over 3500 rpm passing on the highway you should be OK. If the spring change does allow the full 22 degrees of mechanical advance then you will play with two vacuum advance pod choices to suit your driving style.
1) set static/initial timing to 8 BTDC, your spring choice gives an advance of 22 for a total timing at just above cruise rpm at 30...a vacuum pod from a reman/cardone distributor can give you 20 degrees of vacuum or you can try the Vc-208 for 22...(assumes you are not in the 10:1+ static compression range...) for total of 50-52 on the highway.
2) set static to 10-12 BTDC + 22 degrees of advance for 32-34 degrees of timing just above cruise rpm. Use a new VC-239 or a 184/185 for 17 degrees of vacc advance totaling 49-51 on the highway.
It's usually after you burn up 8 hours and 5 gallons of gas in the driveway changing springs and adjusting the fine points that a distributor machine becomes your buddy....
-D.Idiot
