As Rob says, I'm afraid it is extremely unlikely that he will get a place at DCGS. The school cannot even accommodate all catchment children in a normal year.
The extended distance 2 years ago was caused by a change in the rules on address evidence that prevented people moving to the area in the hope of gaining a place.
1. Are these scores out of 199 or 141? I am bit confused.
The score is out of 199, but score is not relevant. Bucks has a fixed qualifying mark of 121, and any child over that mark is eligible to apply for a grammar school place.
If you look at your tube map again, Chesham Grammar is a viable option. A lot of children make that journey from NW London each day.