I found a Wiki on the No.1 but it hasn't been updated since 2006 so there is no mention at all of the .416 Ruger. It seems to be saying that up through 2006, at least, the .416 Remington and .416 Rigby had the AH fore-end except for the stainless version of the Rigby. The 1-S was not produced in .416.

Ruger No. 1 Wiki