I have had this problem with 2 new grills. The best advice I can offer is to drill the holes in the inner fender which bolt to the grill oversized to 3/8". This will give you plenty of movement to swim the grill into place, up/down and in/out.
How does the contour of the top corners of the grill match with the corners of the fenders? I had to remove the screws which hold the tips of the top chrome bar and bend the side support of the grill inward in order to allow the grill to be raised up into position. I did not replace those screws. Didn't seem to need them.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission