Are there any other indicators that may have transferred to the 454 from original motor. Such as the CZ fan clutch and the deep groove pulleys? Will the original intake or water pump tell me anything
From the first pics you provided, that sure doesn't look like an original intake to me, that looks like an aftermarket Weiand. That's why I suggested in one of my first posts that finding an original would go a long way in the "appearance" of the car if selling.
Being a Van Nuys build (no X-codes) You'll have to dig deep to prove this car is what you may believe. Like the others have said, checking the distributor is a decent indicator, not solid, but decent, since they are pretty expensive now to just buy and stick on a clone. It is very possible that things like this and the fan blade stick with a car when doing engine swaps, but no guarantee.
Also it's been mentioned to drop the tank. Van Nuys was pretty good about sticking build sheets on top of the tank. Would only take a few minutes to lower it slightly and take a peek. If you're serious about selling, this is one of the first things I'd do. That's your best hope on a non x-code Van Nuys car. I'd also be pulling the interior apart looking for any clues.
Otherwise, even though it's a neat car, as it sits with nothing much to prove it's an L78 or even an L34-35 for that matter (other than crossmember, radiator, fan blade), it's just another RS Camaro they made 10's of thousands of to most knowledgeable buyers. You would be relying on a buyer simply looking for an neat looking Camaro that doesn't care about provenance, and that hurts the price. Which is why I'm pretty harsh and don't put as big of a price tag on it as some of these guys would. Again though, I'd have to see it in person.
I don't mean this to sound bad in any way, I'm just being blunt and upfront about it so don't take this the wrong way. Because once you put that for sale sign in it, these are the kinds of things you'll get hit with and beat up on.
