Question for Scott- What would be your preferred setup? I like to keep things as simple as possible. I have the big '68ish aluminum Griffin radiator and was originally thinking I would put a shroud on the radiator with a flex fan (simplest),
Yes I agree, it would seem that one should always start with the simplest possible solution first, and then prove that it is going to be necessary for something more complicated, more function failure prone, not to mention likely more expensive (one way or another).
I would attempt the mounting of the largest diameter fan based on space permitting (often in the '66 Mustang it is the lower radiator hose exit from the radiator that proves the first limiting factor we've moved these over 'some' in the past, don't know where yours' is?

); this fan generally of what we used to call an "R.V." style flex fans (deep-cupping blades shovel more air!

) perhaps something along the line of this:
https://flex-a-lite.com/17-inch-silver-flex-fan.html (but do note that they are available in different diameters, and yeah, along with the aluminum radiator a coat of semi-gloss black paint!

); this mounted in conjunction with a well designed fan shroud (if not familiar with what makes for a better design do some homework

); with proper positioning (centering & exposure) of the fan blades in relation to the shroud; then with turning speeds adjusted with different drive rate belt pulleys (note that these fans can produce quite a bit of noise (by-product of moving lots of air!

) at higher turning speeds, but remember your changing the water pump speed at the same time so it proves to be a balancing act

) as the goal is have the fan and pump turning at the speeds required in their respective responsibility in the cooling function, but any faster can prove to produce negative returns, including if only excessive parasitic drag on the engine (less H.P. for turning the rear wheels

); and then some air motion management under the hood, this particularly in attempting to limit the sum of air that can enter the engine compartment and under the vehicle without having had passed thru the radiator (this is one of the major problems of these older chassis, as air circumventing the radiator into these areas decrease the required pressure differential to aid in the air flow thru the radiator!

).
So, the solution doesn't actually present itself as simply as one might have wished, if only as each instance is unique, but often in the effort to accomplish something in the simplest most efficient manor it's mostly just some thought effort, and acquiring the necessary componentry for the execution; oh, and yeah, probably involves a some of "trial & error" too!

Scott.