PROGRESS UPDATE!!
I have just discovered that the problem was a faulty 6 volt 535 flasher all along. I had this old Wagner 6 volt flasher for at least 25 years and assumed it was good. I had this same hyper-flashing issue when I tried to install it on my '40 Ford, but switched to a 5 volt electronic flasher for it and all was fine. When the hyper-flashing problem appeared again after installing it on my Model A, I thought the problem was due to something else, perhaps an anomaly of the world of positive ground. I happened to notice that Snyder's carried a 6 volt flasher that was "Bi-polar". I called them and was told it would take care of the problem...and it did. You'd think after all the years I've spend working on vintage cars I would have learned my lesson about making "assumptions". Exercises like these sure keep me on my toes!
Thanks to all who chimed in with advice. Believe me, none of it was unobserved or unappreciated.