how to determine what engine came in my truck

[truck-collector]

I just acquired a 1968 CST swb that had no engine in it. Unfortunately at one point the truck was repainted and the decal in the glove box was totally removed. Im trying to determine what engine the truck may have come with from the factory. Here is what I know:
It has the turbo 400 tranny.
It did come with a v8 per the vin.
It has factory air and power steering
It is a non posi rear end.

I mention these other items just incase one limits/narrows down the options. Id hope that it was a big block truck, but Im leaning towards the 327. Any where else I should look in the truck-any clues?? Thanks so much.