Perhaps you could apply the decal over top of the aluminum ones that are available - it's as correct as your going to get but as well a more expensive alternative . I do like the yellow border better for some reason . Remember when I compared the original 72 badge - the blue top on the original was definately noticable - it was just blue not translucent blue - like a candy over the silver . So at least the yellow decal is very correct looking - I doubt you could tell the differance but if you don't use the aluminum back - you will have those 2 or 3 depressions in the frame side show up as air bubble or similar and the decal without the backing is going to sit deeper and be detected .
In the end I think the closer you work with detail on these the better off the outcome - meaning stock is what I'm after or try and attain . I am fairly new to this hobby but mature as far as paint and body in automotive field and I like it when someone before me touched something and put back the fasteners as original - paid attention to headmarkings , torqued to specs and used the right products . It's so simple - that's what I enjoy about a good tech forum . I am paying attention to that thread on case cleaning and polishing right now . I have been using scotch brite and being carefull but it needs talked about thoroughly.