I am wondering if it will not overheat in anything over 70 degrees.
Probably no worse then a 67 GT500?
Keeping a 67 GT 500 cool would be a piece of cake by comparison IMO. A mildly warmed over 289 in a Tiger could have cooling issues I can't imagine what lengths you would have to go through to cool even a mild 429 in that small closed engine space . It is not like you could fit a much higher capacity radiator then what is available for a high performance 289 Tiger in it.
There are people who absolutely no hot restarting problems with 67 500's others it's a nighmare. Probably most are somewhere in between.
I don't think the oxigenated gas helps. I think it tends to flash? Could be the big variable depending on where you are in the country since the blends probably vary just enough?
A double thick radiator MIGHT help but it ain't gonna' be cheap. Even so, an 'interesting" concept.