James, the image you show of course uses just leather, rather than leather with a steel strap end. You could either 1) remove the rivet holding the strap end and replace it using the same rivet to secure the strap loop and steel strap end or sew the strap loop on behind the steel strap end. The historical pieces I used to own were all over the map, D buckles sewn into place with no strap loops, D buckles with steel strap ends with or without strap loops, double end buckles ect. The choice seems to have been random wheather late 15th century ( the earliest piece I owned ) or 17th century being the complete arm with pauldron ( this by the way had D buckle on steel mount on the bracer, no strap loop, no way to have one in a very similar manner to the 15th century arm shown on page 37 of FFoulkes " The Armourer and His Craft ) which had no strap loop for the bracers but had an interesting feathure i've seen before on 16th/17th century pauldrons where there is a slot in the top plate of the pauldron just in front of the buckle and parallel to it, allowing the strap from the gorget to come up from under the pauldron to engage the buckle rather than over ( this in theory would allow the pauldron to be pulled up into pretty much direct contact with the upward slope of the base plates of the gorget ).
