The thing is, how many different ways are there of setting up the girdles and caps? They will more than likely all look very similar simply due to the block and crank specs.
Also, have a look at aftermerket RB26 single t/b inlet manifold designs...most of them look very similar in design with slight differences, however, the main shape is quite common amongst almost all. It is even widely accepted and admitted that certain brands are direct copies of the original Japanese designs.
In the end, the consumers will make the choice and the better quality and more reputable products will continue to sell.