[Tibbs]

Once you have the guide plate parallel with the track (or tilted up at the front edge very slightly as Chris advised so the guide post is at least vertical rather than leaning forward) I'd cut a triangular shaped vertical brass fin level with the top of the tube to stand behind the post tube and solder the tube/fin/base plate together. 
...It won't add much weight but add a ton of reinforcement.

Hi Kev,
I've tweaked the guide bracket up and I've added the little spring that came with the guide, I've tested it on a temp Sport oval track which is banked and changes angle to see it it digs in and it runs really nice.
Sorry to be dumb but do you think you could draw a rough sketch of what you mean re support Kev?
Thanks again Chris and Kev, unless you know these things they aren't obvious, especially when you spend loads of time looking at it while making it. Its great to have other peoples eyes some times.
   

Cheers