With the Class 26 grilles made, they had to be fitted into the locomotive sides. I'd already made the holes, filling them up with mash should be easy. Except it wasn't once I started measuring. There are a couple of "issues".
The first is that Class 33 grilles are larger than Class 26 ones. Not much buit a little narrower, enough to be visible if you know what you are looking for.
Second, the original body shell was less accurate than I expected. The grille, and therefore the hole I made, was a couple of mm longer on one side than the other. As you can see from the picture, the new grille would fall straight though !
The solution I decided on was to square up the hole properly and stick the front edge of the new grille in place. This seemed to be spot on for the position I required. Along the back edge a strip of 2mm plstic was fixed in place. I left this proud of the surface and once everything was dry, filed and sanded it back. Hopefully this will hide the repair although I won't know that until the primer is applied.