What is the use of angled plugs? Does the angle help clear headers or something?

That concept actually goes back many many decades...
The idea was to ignite the A/F nearest the hottest part of the combustion chamber...IE near the EX valve it tends to be hotter than near the intake valve...so by igniting the hotter area first it was less likely to have the A/F auto ignite or pre ignite from the hotter side of the chamber.Many car mfgs used that idea long before Chevy did.

And as an added benefit it eliminates 95% of the headers on the market from fitting. So your choice of headers is narrowed do to about 2. :rolleyes: