Mike,
I am going to do a similar thing here with my 70 C50. My truck came without power steering and with a 292 six. When I got it had supposedly a 454 from a late model Chevy pickup (low deck block). Well, I ran the numbers and it is a 396/402 from a 72 Chevelle. So that is coming out. Probably going to take some money from my brothers wallet for that. LOL.
I have just acquired a truck 427 (tall deck) with the correct front motor mount and with power steering pump and bracket installed. I can post pictures when that gets here.
You should know, that there is probably 3 mounts at a minimum, there could be more. Six, small block and then big block. But, small and big might be the same. Not sure. Been years since I was around these daily.
Anyway, will post pics when the 427 gets here.
BaconFarms