Taken from a line across the top of the action on a current 77, looks to me like A=25mm and B=22mm, with the action 16mm proud of the stock. So taken from a line off the stock that would be A=9mm and B=6mm if my maffs is right.
On the standard irons it was a bit of a squeeze for me to get to a comfortable sight line. Have got some peep sights on 8mm raisers which suit me nicely. Big thanks to Phatman (think I've got that correct) who is the fount of all peep sighted knowledge.
http://imgur.com/a/m79J8JX
http://imgur.com/a/1CuHoIk
Be good. And if you can't be good, be good at being bad.