That cargo mat is in excellent shape.
That cloth insert idea looks good. Mine was a Tempest Custom and it had a different pattern than the base Tempest or the Lemans/GTO. I redid mine in a GTO/Lemans pattern as well since I took these photos (I will have to get some new ones), but next time I may go with the cloth inserts as well. The strato bucket seats fit nice as well. When I used to do upholstery work, I installed a set of the older style '65 buckets in a '65 Tempest 4 door, along with a two speed auto shifter and console. Looked like it belonged there except for the steering column still had the place to mount the shifter handle, although the person removed it.