OEM vs Original valve springs etc
 

I will be building couple of early alu case 911 engines (66 and 67), one std and one significantly hotter. I tried searching without luck so what is general opinion of "OEM" parts vs original from Porsche for the following when used on std engine;

Valve springs
Valve stem seals

Are "OEM" ones OK to use or better spend bit more on original ones?
I know some prefer using old valve springs but IMO chances that new ones will last longer is better even if used ones are still within specs.
Of course this sort of list is endless (aftermarket vs original), thus I limited this to two. :D

Thanks!