IMO if you are replacing the OEM header for any UEL catless header your wasting money that could be spent elsewhere.
Just punch the OEM header, it will pass every visual test and you don't need to worry about thermal transfer.
Typically the decated OEM header is as good or better than any aftermarker UEL header.
The OEM header, look at its design specs, pipe diameters, runner lengths, then look at your UEL header choice and do the same. Then read up on fluid and thermal dynamics IRT manifold design.
The UEL header is a carry over from early EJ FI packaging.
From my days playing with STI's one of the first mods was to swap to a EL header, KillerB made some really nice headers that fixed a few typical issues that a UEL header brings up.
Look at every performance engine manifold design, if packaging allows they are all EL, they actually go to alot of trouble to ensure EL, then the diameters, lengths and collectors are designed for your power and rpm goals.
No respectable exhaust builder would concider designing a UEL header, unless it is for packaging.
Marketing and hype around the sound of the UEL header has seen the aftermarket claims grow beyond physics.
If you need to scrounge every available HP and torque then look at a ACE or simular.
Have a read of this for better clarification than my ramblings >
https://www.enginelabs.com/engine-te...gn-and-theory/