1965 Chevrolet Truck GM Heritage Center:
Engine options:
L21 194
L25 292
L26 230
L30 327
L32 283
L39 348
L40 409
L53 DH478
L74 327
L79 327

For comparison purposes:
250 155 hp @ 4200, 235 ft-lb @ 1600
292 170 hp @ 4000, 275 ft-lb @ 1600
283 175 hp @ 4400, 275 ft-lb @ 2400
327 220 hp @ 4400, 320 ft-lb @ 2800

The 292 with a 4.11 rear axle is designed for the purpose of being one heck of a hauling machine.
The 283 and 327 develop their torque at higher RPMs. General purpose, highway cruisers.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."