I can't measure right now but my post #26 is a clear photo from directly above (cab) if that helps. The Diono does not protrude much at all, with the lower seat cushions removed (cab has two lower).

 

is the Monterey 5 you have the same thing as the Monterey 5iST Fixsafe?

 

Yes, it's that exact seat.

 

Wanted to post a big thanks for the OP and the recommendation. Purchased yesterday and this morning was able to take my 5yo (almost 6) out for the first time in the 997.2…


He loved it and the seat is a big success.

Oh, and the 911 is now his favorite car… ahead of a rather well-equipped GLS450 and a couple more “exotic” sports cars. He specifically suggested it be his first car when he’s able to drive.

He’ll get the Volvo instead…

 

Started being on a hunt for a hardback booster for a 997.1 cab which are narrower than the coupe (I had to move the child seat upfront, it wasn't fitting in the back unlike my previous 997.2 coupe)