I don't know the grade of the material but it is magnetic which means it is a ferritic stainless with a high ferrous content. It welds okay but is thin and very easy to burn through.
Re Nelmo's comment above on engine emissions for MOT purposes. You have the advantage of a Q plate which means the emissions test is a visual only. As long a it's not smoking excessively you will be ok.
My mark 3a has inboard front suspension. I kept the original dampers but ditched the springs for 120 lbs one. Transformed the car totally. Better ride and handling. Can't remember where I got them or how much they were but well worth doing.
Regards Dave
Without an air filter you run the risk of dirt being sucked into the carb and the engine. If you can fit a filter somehow then you should. A simple foam type would do.
I think my first move would be to get the radiator turned the right way round. If it doesn't fit the right way round then one that does would be a good move. They are designed to work with the elements vertically positioned.
No matter which RH model (or any kit car) you have or prefer, it all depends on how well it's been put together. I have seen good and bad examples of most of the models over the years. Each individual car needs to be judged on its own merits.
My 3a was first registered in 1998 and just missed the introduction of IVA. It also has the advantage of a Q plate which means the emissions are visual only. Its not a problem as all in good order with no visible smoke. It is rather nice to know that no one's going to stick a sniffer tube up your exhaust pipe. It usually takes my guy about 15mins to test with me in the car as he is a little on the plump side.
I have a 3a with inboard coils. The standard/lit supplied springs are much to strong. I thing they are around 300lbs. I replaced than for 125lbs ones and the difference in ride comfort etc is amazing.