I myself would recommend checking to see if the stock mounts are tight and that the engine isn't to one side more. (Keep in mind that left steer rear wheel drive cars are offset to the right for the steering shaft.)
Putting urethane or solid mounts on a voodoo is definitely going to increase...
That's easy.
537 rwhp with....
Tune
Gas
Headers and x pipe -20 pounds
Forgeline GA1R and Sport cup 2 tires -52 pounds
Rear seat delete and Trunk junk -32 pounds
Braille battery -20 pounds
These alone will drop 124+ pounds.
I've removed over 200 pounds with Recaro spa profi...
I have R springs and 305/30ZR19 sport cup 2's on my track pack with 11x19 forgelines. The R springs lowered it 1/4". The tires lowered it another 1/2" plus I have the R splitter which extends forward quite a bit more than a base/tech/track splitter.
I have the Ford springs coming soon and "MAY"...
I have ARH long tubes and was the very first to prototype them. It's hard to tell by your picture but mine has over 3/8-1/2" minimum at its closest area. If the person that installed them didn't tighten the motor mounts or if the engine moved off center that would certainly cause clearance issues.
I have ARH long tubes and don't have a single issue with them. Are you certain who ever installed the headers tightened the motor mounts after installing the headers. Also if the engine / headers are making chassis contact your knock sensors will pick this up and retard timing and reduce power.