I tried to find pictures of my front bumper under construction.
If I find them Ill post them but, essentially took cuts out of the bumper in some places, and used metal foil tape as backing to build new fiberglass on to fill the few inch gaps that were needed.
Next, once it was all one piece again, took curf cuts out of it in order to expand the profile of the end of the bumper to meet the flare exactly properly.
Again, created new fiberglass in between
(also, note that the factory SC-CR car had a bumper that did not match the flare - it was a limited run of race cars using off the shelf parts form different models, and fit dint matter much on race cars back then, I doubt that is what we are looking at in your pic though

)
Unlike the bumper, here are pics of the MA shaw fenders fresh out of the box with no rework
(bumper needed a bit of love)
You might be able to find a pic on my build thread
Saving a 73 from the crusher...