Somewhere, I've got an AMCO ad showing the 'Vista' grille; but I don't recall seeing those bumper add-ons in there. Might be the bumpers really were from Shelford, and the grille from AMCO.
Local club member has one of those grilles on his TR3A, it looks much better to me on his car than it does in the photos on eBay. In fact I bought one myself with the intention of rechroming it, but never found one of those round tuits.