Yes, if you're willing to put in the work you can convert an original trilogy helmet into an Inferno. I did that with two for my wife and I. Gist is this:
* Reduce trident size, align with lip on forhead helmet.
* Cut rectangular indent into trident.
* Only have the one greeblie on the left side.
* Fill in any and all gaps between the face and the helmet.
* Mold oxygen mask connectors near the ears.
* Cut out eight teeth and back with mesh.
* Use appropriate greeblies in the hose ports.
* Attach pillbox if you don't already have it.
* Use Imperial greeblies without a notch.
* Use an appropriate red lens.
* Paint Mowhawk, stripes, symbols, teeth, vocoder appropriately.
Ours were originally RS Propmaster helmets, and they converted beautifully into Inferno, with a decent amount of work of course: