I have looked at the Frosts page https://www.frost.co.uk/paints-coating-plating/automotive-paint/rust-paint-treatment-solution.html
If I am reading correctly there are several manufacturers. POR-15 (well known), Eastwood and Granville. The considerable range of offerings hardly helps on selection. Does anyone have the experience to help?
Then of course, there are subsequent treatments - I have cans of two Dinitrol products, so that isn't (should not be) a problem.
The project is the engine bay of the 21 where there is flaking of the original powder coating, surface deterioration and general tiredness.
As it is a special car, there being just 48 of them, it is worth doing a proper job.