Posted: 25/09/2015 at 09:37
firstly, you cannot cut into old wood. Always cut leaving a green shoot or two on each branch. I don't think you are going to be able to trim back to 3'.
Your neighbour's side may remain green but you will see only brown wood so you need to compromise. Talk to your neighbour...he seems to know what he's doing.
try to aim for an angle...a slight narrowing from bottom up so the top is narrower.
I think its a bit late now if you are in a cold area so best tackled in spring.
new growth is quick, esp in spring.