Keith,
You would do a lot worse than to join the GT40 Enthusiasts Club. The points you raised are addressed regularly and there are up to 3 different monthly area groups within reach of London where you can discuss problems and look at solutions on members' cars during summer months.
Specifically,
1. My GTD radiator let go in a big way the day after getting back from a 1,000 mile French tour last September. As Julian mentions, Mel Johnson built a radiator on a phone call for £346.63 inc VAT and Brian Magee made a beautiful job of fitting it, including a dynamic bleed from the bleed valve back to the header tank. This cleared trapped air problems that all mid-engined cars seem to suffer from.
2. The perspex covers do scatter a lot of light. You can partly get round this by fitting high output bulbs; they may need a p45t to p43t adapter, but we know where to find these.