26" stock radiator or 26" aluminum ??????

AFCO makes a nice affordable 26" aluminum rad, highly impressed with their prices and products.
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If you're maybe thinking about getting a custom unit:

The "ideal rad" for a high-performance small-block (including 406/408 strokers & air conditioning) Mopar engines, in terms of cooling as well as weight, would be a 26" single row with at least 1.25" (1.5" preferably) tubes.
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Check the entire AFCO catalog to see if they now offer one as described,
off-the-shelf, as a non-custom unit.

Ditto for checking the MODINE catalog also.
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Don't forget a well-sealed shroud, high-perf electric fan, high-quality WP and T-stat are all also necessary to complete your cooling system.

HTH :)