Well finally found time to again test fit the repro front bumper I bought a few yrs back. It came with holes for fitting the rubber strips and over-riders. I bought all new rubber strips at the same time.
Its tip to tip inside dimension is 1503mm, whereas my original is 10mm wider. On my initial test fit I had been concerned it was too tight and so had set it aside for another day. This time around, however, after applying lots of protective tape and very gently pushing the panels inwards just a little at the valance/sugar scoop bolt-up joint lines (on my car they tend to bulge there slightly) to gain a few precious mm, I found the new bumper slotted into place better than I'd expected. (It's still too close to the bodywork on the RH end, some more careful massage work is required there. LH end is fine now).
My original bumper has no doubt taken its share of knocks, and has already been re-chromed, so who knows how 'true' it is. Years ago the number plate and its brackets had been bent inwards, and my bending the brackets back into place - rather crudely - had stressed the metal and the chrome had crazed so that is why rust has developed. My bad.
But the new one is now on to stay! Am quite happy with the result. It wasn't a plug'n'play in my case, took time due to the vagaries of my particular car. I had to slot some of the holes for the fixing bolts of the rubber strips so they would comfortably fit without stress around the curves. (Maybe the rubber had shrunk while sitting in storage). I also slotted the holes for the over-riders so they could adjust to line up better.
The bumper came with an extra pair of holes top and bottom and inward of the over-riders, for bumper-mounted turn indicators I presume. Redundant in my case, I will source some chrome blanking plugs.
Before its final fit I also painted the back of the new one with a generous coating of silver cold galv to keep it good.
My 2c worth FWIW.