Denny,
The first of your links in response to my post demonstrates that even a PHD can be guilty of passing on inaccurate information when the subject matter is outside of his area of interest. His organization's primary objective is in the area of pollution, not automotive mechanics. The second one from Australia about Rolls Royce however is very well written. The only major item of conflict there is a function of the U.S. way of doing things vs the European model. We actually measure octane rating three ways; RON, MON, and then whats posted on the pump, each of which come up with a different number for the same fuel sample.

The real issue with low octane rated fuels is detonation (autoignition). Here's a link to a well defined difference between the two. http://www.misterfixit.com/deton.htm
As I said, it was a small nit. Preignition can in fact lead to detonation, and the causes of each can overlap. It is very possible to have both in the same engine, but they are separate functions.

60nut. Octane requirement is an empirical thing. 10 to 1 on a flathead seems high, even 9.5 considering the relieving, but let's say you're right. Think of octane requirement as a heat resultant thing. The higher the heat in the combustion chamber, the higher the octane requirment. Your aluminum heads help keep the temp lower, the exhaust routing on a flathead keeps it higher. Combustion chamber deposits increase temp. A poor cooling system (or corrosion loaded block) increases temp. The article in the link above denotes a number of other contributors. In other words, damned if I know what your needs are. It may be that you can get by on regular grade, especially in a light weight car like a T bucket, and if you don't ever put a big load on it (e.g. racing, towing, etc.) If you drive in high ambient temps that will increase the octane need, so your requirement could be different seasonally. And as you said, it's hard to hear it ping in an open roadster. And if you're like me, your hearing has deteriorated to a point where you may not be able to hear it anyway. If it were mine, I'd buy the higher grade just for insurance sake, even though it may not be providing any additional benefit. If you're obsessive about it, find a tune shop that can attach a knock sensor and can simulate your highest operating temp situation and test for detonation.