Well I finally got the time to root around my 73 F350 CC longbed that I bought in April and I was underneath the truck looking at the bottom of the eng and I see a ID tag on the side of the block that reads AC DELCO Engines, Remanufactured for General Motors, it gives the Bore and stroke, main bearing, rod bearing specs. This is a FE390 eng because I have 3 of them and I know what they look like but what I'm confused about is why that ID tag is on the side of the block. GM & AC DELCO did not produce 390's. The only thing I can think of is the previous owner had trouble with the eng and took it to a GM dealer and they ended up replacing or rebuilding the eng and when they were done slapped there ID tag on the side of the block. Does anyone have any insight on this?

not uncommon for this type of work to be done

I would like to know how you can tell it is a 390 by just looking at it as 352 and 360s look just like a 390 externally

Yes you are right 352, 360 & 390 all look the same, what I meant to say was I can tell what a FE eng looks like just by looking at it. I just have never seen a remanufactured engine for Ford from a company that deals with GM only like AC Delco. Learn something new everday.