Is 27" from outside to outside flange/legs or inside to inside where the radiator sits? What I have is, Outside flange measurement is 28 3/4, inside to inside is 26 and bolt hole center to center is 27 1/2There is one on eBay https://i.ebayimg.com/images/g/-8gAAOSw1vllYPVJ/s-l960.webp and it looks just like yours, you have the correct one now. I think the 3rd rib that SSpev is seeing is just the flared opening. The shroud mounts to the 6 same bolts that hold the radiator in. They are 27" across. This is the same on 6 & V8 cars. I looked at a shroud I have and it is the same. I have 2 of these. Without the mounting flanges/legs the round part is identical top & bottom. The mounting flanges determine top & bottom as they are offset vertically from the fan opening.
Jeff 3/4