[Brad54]

That part number on the package shows those are hydraulic roller lifters.

Look, we don't mean to be dicks, but NO Chevy engine came from the factory in the '60s with a roller cam. It just didn't.
I had a VERY good friend who was a factory-backed Super Stock and Pro Stock racer in the '60s and '70s... he was so good, he was one of only 69 people to get a 1969 ZL1 Camaro, which is the most desirable Camaro built.
He raced a 327 in the '70s... he did not use a roller cam, because it didn't exist then in factory applications. If it did, he'd have run one.

So I think what's happening here, is that your engine shop is screwing you.
To convert an engine over to roller cam, there's a lot you have to do to the heads--they'll have to elongate the pushrod holes, machine the rocker stud bosses for screw-in rocker arm studs and pushrod guide plates, and machine the spring pockets to accept the larger springs required to run a roller cam.

I know, because I've documented all that work on a set of double-hump heads of an engine I built.

That work is going to add a BUNCH of money to your machine shop bill.
If those things have NOT been done to your heads, there is absolutely no way it is an original roller cam engine. A roller cam MUST have those things, or the engine will destroy itself.

Going forward, it seems very, VERY unlikely you have a high-horse corvette engine in front of a 2-speed PowerGlide in a '66 Truck.
I wouldn't be surprised to see double-hump heads, Everyone thinks that automatically means Corvette, but it doesn't.
But as someone else pointed out, if it is a Corvette engine, it will have to have an aluminum intake and 4-barrel carburetor.

I don't want to be a dick, or the bearer of bad news, but I suspect your machine shop is being dishonest.

Get pics of the unmachined heads (the part under the valve cover, not the side with the valve faces in it), the stamped numbers on the block on the head surface next to the timing chain cover, and a picture of the intake manifold and carb that was on the engine.
Do those things, and that'll tell the tale.

I'd ask him for the original lifters and camshaft, too--it's obvious if it's a roller or flat tappet. But if he's being dishonest, he'll say he threw them away or threw them in the scrap barrel already. OR, he could just pull out some others from a different engine and say "these are them." At which point, you'd need to photograph any part numbers on them, and that's going to open up another can of worms because he'll say "Oh, I grabbed the wrong one," or or or..
Take a pic of the heads. ASAP. From all angles.
-Brad