TooMany62, excellent post. I dug in and have some examples I found in the research. First the "standard" most of us have tried or used:

Hayden 2765
Overall Height 2.67"
Standard Clutch - 60-70% Fan turn when engaged.
Use with 1 1/2" pitch fans

Here are some heavier duty alternates that are 5/8" to 15/16" longer:

Hayden 2747
Overall Height 3.34"
Heavy Duty Clutch - 70-90% Fan turn when engaged
Use with 2 1/2" pitch fans

Hayden 2797
Overall Height 3.65"
Severe Duty Clutch - 80-90% Fan turn when engaged
Use with 2 1/2" pitch fans

On my E-Body, I could easily fit either one into my application but the 2747 would be a cleaner fit. This would give me 10-20% more volume at idle plus it would put my fan deeper in the shroud where it needs to be. I could possibly fit the 2797 which would give me 20% more volume but I may be a tad too deep.

If the solid fan works for me, I am going to measure again to see how the severe duty would fit. All three clutches are available locally so it would be a great test.

Just installed a fixed fan in my 440 Cuda and it has reduced my idle temperatures. My radiator now cools the water by 11-17 degrees at idle instead of 5-10 I was getting with the clutch fan. More importantly is the fact that my car now equalizes at a reasonable temperature at extended idle and I don't think it will creep up out of control.

I notice no sound difference whatsoever when driving but I have the windows open and car is pretty loud anyway.

Tried the Hayden Severe fan clutch to get that 80-90% shaft speed but it just won't fit right so I got the Heavy-Duty (Hayden # 2747 ) to get the 70-90% shaft speed. This will be a good improvement over the standard #2765 which operates at 60-70% shaft speed when engaged.

As you can see, the Heavy-Duty model is a little over 3/16 taller than the standard but for my '70 E-Body with a 440, that will be close enough.