Using two stock light springs in distributor advance, good idea?

Usually not. Most people have the best luck leaving the stock light spring in and coupling it with whichever aftermarket spring works best. Sometimes it's the lightest aftermarket spring, sometimes not. It's all combination dependent. I leave the factory light spring in and replace that big battleship factory spring with the lightest aftermarket spring as a start. So far, that's what I always end up with. Probably because None of my hot rods have been heavy like a B body. My 75 F250 I used the lightest and heaviest aftermarket springs and got the best result. 99 times out of 100 you will end up with a mismatched pair of springs to get the best result. I know I always have.