'65 Barracuda with a '71 340 needs a Radiator...

The "factory" would have put a 26" multi row copper rad with trans cooler.

Assuming you water pump inlet is on the passenger side, a center inlet to the rad and passenger outlet would be a slant 6 with a/c and trans cooler that is 26" wide would be what you would use. But your core support is only set up for a 22" wide rad. So you would need to modify it to use a 26" rad.

Option 2 : a 22" super cooler rad without trans cooler .
Use a plate style trans cooler in front of the rad.
Use a shroud with at least 2500 c.f.m thermostat controlled electric fan(s) also a fan override switch.