Any mechanical performance mods for 6.4?
 

I'm very familiar with Mustangs and not as familiar with turbo engines. In the Mustang world, the performance mods are mechanical (heads, cams, cold air kits, exhaust, intakes, etc) and then tuning is kind of an afterthought - although still important.

Are there any popular mechanical performance mods for the 6.4 or is everything just emissions deletes and tuning?

Turbos, dual fuel pumps, injectors, upgraded pistons, cams, ported intakes, built transmissions. Both worlds require hard parts to go big. If you want anything over 575hp, hard parts are necessary. These motors are capable of big numbers. Just got to spend some coin.

A lot of guys are putting down close to 600 RWHP with a cat dpf delete, cold air intake and a tune...

That's a good reason to not bother with anything else!

BUT some of us have to deal with emissions and removing that stuff is not an option. What about 50 state (or even 49 state) legal mods?

They exist but don't give you that "wow" factor.