A quick thing you could try is to lower your saddle just a bit, then try to pedal with your heel cups, relaxing your ankle as much as possible. If you think about it for a minute, you'll see that, having a super stiff shoe sole, it doesn't matter where your cleats are, only what you do with your ankle in terms of putting pressure on that toe. If while pedaling with your heels, your knee angle is too small, lower the saddle until it feels right again. Looking in a mirror while pedaling, the bottom of your foot should be level or even a hair heel down. Adjust until that's true. I realize that retraining one's pedaling after decades is not easy.