Do you have access to some sheet metal, a bench vise, and a welder? It's a relatively basic fab project with some .050" sheet steel. Use some tin snips to trim the piece to width for the circular part that surrounds the fan, leave a 1/2" or so lip to bend over 90 degrees to weld to the flat sheet. Make the flat sheet big enough to pick up the attach points on the radiator flange, match-drill it so it bolts up in the stock locations. Cut your big circle in the flat sheet so it clears the outer edges of the fan by an inch or so all the way around. Bend your first piece in gradual increments so it matches the radius of the hole in the flat sheet, seld the edges together so it's like a really short tube. Snip and trim one edge so that you can bend about 10-12 1/2" wide or so flanges over to weld to the flat sheet. Radius your corners and remove the sharp edges with a file so you don't cut the snot out of your hands while working with it, weld it up, paint it, install it.
Or you can do a partial fab same as above but picking up part of the existing piece of shround you already have.