Your Biopace double 42/52 is likely on a 130 BCD crank and the rings from your MTB are probably on a 110/74 BCD crank. Not interchangeable from one crank to the other. You might be able to find some smaller 130 rings for the road bike, and almost certainly find larger 110 rings for the MTB, but your choices will be limited. I think I still have larger 44/50 rings from a 110 BCD triple touring crankset.