[Kevan]

The other thing I'd change is the gap between the bottom of the plate and the top of the guide is possibly going to make the guide wobbly side to side, I like very little horizontal play on a guide post.

If that was my car I'd either solder another flat brass plate (with a hole) underneath...or move the whole thing down at 45° so the guide is right up to the plate when the front tyres are sitting on the track.