With the ribbed block, it's probably a 391 Industrial engine. Ford put 410 pistons in them to lower the CR, the pistons don't come up to the deck at TDC.
That said, I've seen a few 390 pickups that were 410's when we pulled them down! I guess Ford had a bunch left over and passed them off to us Canucks because they never smog-certified them in the 'States. So if you hear of a "390" pickup, about a '74, '75, that has more go than it should have, this might explain why.