Advice on navigating header clearance issues.

Denting should be the very last resort.
Loosening motor mount bolts, shifting engine, re-tightening bolts, shimming, shifting trans mount as possible
A ratchet strap carefully around trans or frame/torsion bar to "encourage/bend" the collector over.
A fence post up the collector with a nudge to gain clearance.(careful not to knock the car off the hoist or stands.)
Change the head flange angle that the tubes leave the head by belt sanding/filing as nec to gain clearance as needed.
And before final bolt up, make sure the head flange is fair/true flat so you don't end up bitching about flange leaks needing new expensive "cometic" gaskets to seal.
Easy peasy.
You might find doing a "search" helpful to find a number of install threads.
Good luck .