What is the correct height picatinny gas block?

[purplepack]

I am going to remove my standard A2 sight to mimic the optics ready version of the AR15. I am going to use a sightmark reflex scope and my question is what height does the gasblock need to be in order be sure my sights all line up?

AR-15|AR15 Gas Blocks and Gas Tubes

 

[purplepack]

Secondly, would one the flip up front sight gas blocks from yankee hill give me the height I am looking for?

Gas Blocks - Firearms Accessories | Yankee Hill Machine

 

[ChattanoogaPhil]

Choose "same plane" to match with a standard height rear sight.
"Same plane" means it's the same height as the rail on your receiver.

 

[sgtsandman]

I agree, you want "same plane".

 

[Rastoff]

Secondly, would one the flip up front sight gas blocks from yankee hill give me the height I am looking for?

Gas Blocks - Firearms Accessories | Yankee Hill Machine

Yes. This is the one I would get: Front Flip Sight Tower, Standard w/o Bayonet Lug

If you want just the gas block, get this one: Railed Bull Barrel Gas Block