What would you pull off this C Body for your A Body???

The 26" radiator will bolt in with a few extra holes in the radiator support, and no cutting is absolutely needed. I installed a 26" 3 core Champion radiator in my '74 Duster, all I did was drill 4 holes and weld a couple of nuts behind the top holes, that last bit isn't even necessary, just for ease of install as I'm usually working alone.

Cutting the radiator support for airflow isn't necessary. Yes, you will get better/more efficient cooling if you open it up to 26". But, the outer parts of the core and cooling fins are exposed to air even without cutting, and they will still transfer heat just fine. Regardless, the additional cooling surface will work better than a 22" radiator.

And I would still pull the 8 3/4. The axles can be shortened to A body length, same with the housing. And if you've seen the price of A body 8 3/4 rears lately, you might even be able to get all that done cheaper than finding and buying an A body 8 3/4.