Are you sure? I think those look right for big blocks. Of course the colors are all wrong, but the manifolds look like my '70s originals. [Edit: Just saw I was the third person to say that, sorry!]
In my teardown I didn't find much in the way of chalk marks on the firewall, I'd be curious to see what anyone has for photos of originals that still carried them. Unless the assembly line process was different enough from the cars that they didn't use them.
I'm not aiming for Pebble Beach style correctness, but still trying to make it look stock. So I use shiny bolts where they would have been painted and so on, so don't panic when you see the photo, I'm not claiming its 100%. Still, to me one of the biggest things in keeping the engine looking original are:
1) Correct paint sheens. Most black things underhood are 20% gloss, but the radiator is different (high gloss) and so on
2) Correct clamps and hose fittings and so on
3) Clean everything (check out my clutch fan in the pic below, it was seriously ugly, and that's just a lot of time with a toothbrush)
4) Correct stickers
5) Correct plug wires, correct distributor cap (not HEI), looms, etc. Mine are even Packard wires, though not date coded (I'm not that hardcore)
...and a personal peeve, but one of the most important:
6) If they didn't make or use it in 1970, don't use it. That means no zip ties, as handy as they are. No corrugated plastic wire covers, yellow 10mm plug wires, and so on.
Although not always correct, I'm a big fan of "contrast". That means different colors on different parts, different gloss levels, and so on. That's why my shocks are blue below (and because the original GM shocks I've seen were blue) and you'll see about 8 different finishes between the control arm and the spindle. From the factory it'd probably just be all black, but I'm into the variation.