Do all A bodies have overheating problems?

I'm pretty sure the ratios will be fine. Besides there are not a lot to choose from in the stock category.

Like I said; beg borrow or steal one of those gigantic direct drive 7 blades.
Test it to prove the problem.
If that cures it,then you can start looking for something in-between.
Here's the fan with the wrong clutch;
MOPAR 7 Blade Fan & Clutch, # 2863216 Charger, RR, GTX, Bee, Cuda, very nice | eBay
Heres the right clutch
NOS MOPAR 3462182 fan clutch max cooling Cuda Challenger Charger Road Runner GTX | eBay

You don't have to buy these pricey items.
I bought a THERMOSTATIC clutch from the Ford dealer for like 70$Can in about 2002. It was off an early 2000s F150. It works better than any Mopar clutch I have ever had.
The fan you can probably score used somewhere for maybe $20. I think they were oem on A/C teenerDarts. There should be a bazillion of them out there by now.
Hayden - Fan Clutches and Fan Blades