David
The only thing that would, in effect, change the distance between the ends of the bonnet would be an alteration to the rake of the grille since the bulkhead end doesn’t move. Have you had the grille off as well as the bonnet?
it may be easiest to loosen all the screws and bolts that hold the grille to the wings and side panels, fit the bonnet and then tighten all those fasteners up with the bonnet now attached.
Not saying this is what it is ….but this is what I did with a similar situation a while ago.
regards
Paul B