You are going to want to go with the 642 gasket for your 06' Outback.
The main differences between the 2 are the location of the coolant passage openings and their shape.
All '06 + EJ255 (WRX) uses the new HG. All '07+ EJ257 (STi) uses the new HG.
They also of course revised their cylinder head to match the the new openings. (chicken / egg)
The 642 gasket lines up these openings much more in line with what your cylinder head needs vs the 770 gasket does.
770 details:
Gasket - https://parts.subaru.com/p/Subaru__/GASKET-CYLINDER-HEAD/49223398/11044AA770.html
Head -
Gasket on Head -
642 details:
Gasket - https://parts.subaru.com/p/Subaru__/GASKET-CYLINDER-HEAD/49223394/11044AA642.html
Head -
The main differences between the 2 are the location of the coolant passage openings and their shape.
All '06 + EJ255 (WRX) uses the new HG. All '07+ EJ257 (STi) uses the new HG.
They also of course revised their cylinder head to match the the new openings. (chicken / egg)
The 642 gasket lines up these openings much more in line with what your cylinder head needs vs the 770 gasket does.
770 details:
Gasket - https://parts.subaru.com/p/Subaru__/GASKET-CYLINDER-HEAD/49223398/11044AA770.html
Head -
Gasket on Head -
642 details:
Gasket - https://parts.subaru.com/p/Subaru__/GASKET-CYLINDER-HEAD/49223394/11044AA642.html
Head -