Is this a 4-1 or a 4-2-1 or is there an option for either. My plan was to get a Mugen 4-1 or a Spoon 4-2-1. But I am still undecided.

Mugen has a Diameter of 45mm-50.8mm-60.5
Spoon has a 52mm on their one piece 4-2-1 Header and 42.7mm-56mm-60mm on thier 2 piece 4-2-1.
Most of the other JDM manufacturers use the same measurements as Mugen for thie 4-1 designs.

All are ranging about 900 and Up. The OEM Header is an excellent piece just that the weight is it's only down fall, but you will have to shell out a few $$ for a good quality lightweight header.