Dafydd
Are you looking for chaired track? - rather uncommon on NG lines?
However I’m a member of the SSMRS- former secretary. But I’m down in Buckinghamshire.
For flat bottom rail, I suggest Kalgarren rail which is correct section with the height equaling the width.
Are you aware of O-21 Facebook group. Where you find myself, Keith Fothergill and Toby Jones who is doing some magnificent modelling of the North Devon & Dorset clay lines.
best regards
Stay safe
Stay sane
Kelvin
