Well.... I can help on the prep..and look fwd to answers on fitting!
I've never fitted a set... only removed

As far as prep to get a match front and back...

Any mold blemishes/bubbles can be filled with bondo...then sanded.

Then, overall Wet & dry sanding is best, I'd say 150/220 grit initially both front and back plates

Then, a couple of good coats of primer , hi build is great, and sands well.

Once primer is REALY dry on both, wet & dry again with 220 then 400.
Edges are tricky, as primer will 'sand off" fast..so beware!

A properly sanded 400 finish will be perfect for top coat application.

Rattle can is fine, just build up layers carefully to avoid runs.
Final finish coat should be an even , overall 'wet' coat to ensure uniform look.


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Regarding template/fastners etc... I'm interested in ideas too!

As per PM's we traded Earl.. people seem to mount plates in different ways.
Some give them an all round riveted/bolted look..but some of these are 'faux' and simply cosmetic. Others drill cladding.
Front plate will attach through centre and into the bolts holes for the license "blank".

And I'm afraid thats about the extent of my knowledge on these!

Maybe Kat or Dub or..?? anyone thats fitted new plates can chime in

Hope so !

Jo