Definitely use OEM studs and nuts. I used Fel-Pro studs, while the studs themselves were fine, the nuts had a 5/8" head and metric threads, instead of the 14 mm head size. It was a nightmare as the install was way harder as there is hardly any room to work with the 14 mm head size; 5/8" is bigger and makes things even tighter.
Since you have a 05+ GX with the VVTI motor get Fel-Pro manifold gaskets. They are Japanese-made multi-layer steel and are identical to OEM, at half the price (probably form the same factory). However, the 03-04 Fel-Pro non-VVTI gaskets are not OEM MLS and lower quality, and similar to the junky manifold gaskets that come with the DT headers (as jiggletits found out). The DT collector gaskets are fine to use on their own, and easy to replace in the future if you ahve a problem.
I would also recommend a SAIS bypass when you install the headers. You can then skip reinstalling the SAIS tubes from the header to the back of your engine and make a blockoff plate instead (I made a plate out of 1/8" aluminum flatstock, then sawed off the flange on the SAIS tube and bolted it to the header, with the plate sandwiched in the middle, using exhaust cement for sealant). Several folks make the SAIS kit; I used a slyfox75 kit from eBay and have been very happy with it (but it looks to no longer be on eBay...).
Since you have a 05+ GX with the VVTI motor get Fel-Pro manifold gaskets. They are Japanese-made multi-layer steel and are identical to OEM, at half the price (probably form the same factory). However, the 03-04 Fel-Pro non-VVTI gaskets are not OEM MLS and lower quality, and similar to the junky manifold gaskets that come with the DT headers (as jiggletits found out). The DT collector gaskets are fine to use on their own, and easy to replace in the future if you ahve a problem.
I would also recommend a SAIS bypass when you install the headers. You can then skip reinstalling the SAIS tubes from the header to the back of your engine and make a blockoff plate instead (I made a plate out of 1/8" aluminum flatstock, then sawed off the flange on the SAIS tube and bolted it to the header, with the plate sandwiched in the middle, using exhaust cement for sealant). Several folks make the SAIS kit; I used a slyfox75 kit from eBay and have been very happy with it (but it looks to no longer be on eBay...).
