Obviously, any 400 1st gen will be worth more with all it's original parts. If you don't have the originals, the next most desirable thing is to get replacement parts with the correct casting numbers & date codes.
But, if the numbers don't match, a 455 will be worth just as much as a 400--more in some cases. For example: a later model 400 with a 500557 block will be worth much less than a 455, to most informed Pontiac guys.
And, a base model '67, which doesn't have it's original engine will be worth more with either a 400 or 455. IMO
But, there are a few purists out there, I suppose, who would prefer to have an OHC six, or 326HO, even if they were not original. Tastes differ.
"...If it is a 400, is it still worth more than a base model with the mods?..."
Yes ! Because it looks clean enuff to restore with the numbers correct parts. Done correctly, it would probably bring $25k-$35k.
As is, I'd guess $12k-$15k. Looks to me like it would be a bargain at $10k. If I had plenty, I'd go $10k on it myself.
"...How can I confirm if it is a true 400 or a fake?..."
