Oil... Can I go from synthetic to non-synthetic?

[tirebird]

I have always used Synthetic in my T/A and GN. I'm convinced the science supports the choice. But there are skeptics one of whom recently was brought over synthetics while installing a new MSD distributor in his Chevelle. The break in tag on the distributor warned against using synthetic oil during the distributor break-in period. A light went off in his head and now uses Mobil 1 in his car,..after he broke in the distributor gear using Valvoline dino oil.