As of right now the steam knight mask cannot use the Helmet Front accessories. I could understand why if most of the items clipped with it in poor ways. However, it is roughly the same shape as the Jelly Helms and they can use front accessories.

I actually went through the trouble of testing a bunch of the Helmet Front accessories on the Steam Knight mask and most of them (as expected) work quite well. The only ones with major clipping issues being the pipe and mustache.

If the sole reason the Steam helm cannot use front accessories is due to those two items, then I implore you to alter your decision.

Here! I tested front accessories on the Steam Helm and honestly they look pretty darn good.

http://i.imgur.com/xMd7u.png - the vented visor accentuates the slotted holes on the face in a sort of cool way. Reminds me of Star Trek.

http://i.imgur.com/lN5LO.png - the goggles actually clip in a cool way. making them look very grim and spooky and fantastic.

http://i.imgur.com/xrLYL.png - the binocular visor doesn't clip at all and makes the player look quite robotic. (arent the knights robots anyway?)

http://i.imgur.com/9Pz1H.png - knight vision goggles look basically the same as they do on all the other helms

http://i.imgur.com/dgchk.png - helm mounted display clips a bit more than the others at the very front. still looks cool.

http://i.imgur.com/3dQzC.png - all the glasses and eyebrow accessories dont clip in the slightest. and are funny to look at.

And if you combine some side, top and armor accessories you get a very cool very macho looking knight: http://i.imgur.com/EQ2uv.png

Please 3 Rings. Don't leave the Steam Knight Helm (and Skelly Helm as well) users unable to use Front Accessories just because the 'mustache' and 'pipe' clip badly with the face. Everything else looks great, as I have shown. 2 items should not negate a whole category.

Pretty please with sugar on top.