Difficult decisions TJ, the most difficult thing is to choose between originality and something that is considered an improvement, and with modern technology available it is all so easy to 'improve'.
Unfortunately that is completely up to you. I know it is very tempting to improve on the original design, but how far should you go? Same as your previous question a couple of posts ago on the clutch...
I am personally sticking to originality as much as possible, I believe that is the true value of these cars.
So, I have the original clutch in my car.
And yes, I have used felt for the tank straps, I did fully soak it in undercoat/rustproof oil to hopefully prevent it from holding any water. Main thing is to have the very best paint layer on your tank as possible. Imagine using another material instead of felt, and finding out later that this material has damaged your layer of paint.... hard to stop corrosion.
But, yes I agree, cork or rubber could we a good material. But remember, both these materials were available when our cars were designed, why did they not choose to use it? Maybe it is not an improvement? Who knows,
Get in touch with Marles, the man to speak to is David Cornwalles, great guy! Might be more expensive for you getting the parts from the uk, but David will not let you down and he will help you with the parts you need.
Not an option Unfortunately. We are not talking about Gemmer or Adament steering box, and even for those I doubt if Afra has anything for them. When it comes to Marles, Afra does not have a clue what is inside of those. Trust me, speak to the man who has built them, and the pricing will at least be fair.