are there any headers that are direct fit to factory y pipe?
as in to remove the stock manifold and replace with header? what about donut gasket?

No. And why would you want to use the LG4 Y-pipe which is restrictive to begin with. Note the LG4 Y (one on the left in the pic below) compared to the L69? What kind of performance would the former really offer?

https://www.thirdgen.org/forums/atta...tion-ypipe.jpg

JamesC