4" Concrete Boundary Post Brackets

[woodchopper]

Have three concrete boundary posts separating mine and the neighbours gardens.
Am looking to replace the fence by bolting on 4"fence posts, then add "D" rails and finally 6" x 6ft fence boards vertically.
Is ok to do this on the end two posts but not the centre one - the holes through the post are from side to side whereas the end to a in both directions.
Is there a bracket available that would enable this - or does anyone have any other ideas that would leave me as much garden as possible ?
Was looking at Arris rail brackets but not having got one physically I don't know if they would do.

[vulcan42]

I had this problem some years ago, on the concrete posts where the hole goes through the side, I used long bolts and bolted 3"x 3" timber posts either side. I was then able to screw the D rails to those. A word of warning, leave good gap between each vertical board. I didn't and during a storm the wind couldn't get through quick enough and it toppled the fence, breaking the 4" CONCRETE posts.