04 tahoe swap....manifold question

[68chevystepside]

I have an engine out of a 04 Chevy Tahoe i will be installing in my 68 stepside. I noticed the manifold that came with the engine has two holes for sensors? one towards the front and one towards the back. the back hole is for the sensor pressure but i have no idea what the hole on the front top of the manifold is for. I tried looking up the new dorman manifold for the vehicle and it doesn't have any sensor holes on top. can someone explain this. thank you

https://www.oreillyauto.com/detail/d...oe?q=intake+ma

https://imgur.com/qMKRZgj
https://imgur.com/gZklXON
https://imgur.com/L7Z2yNY