By the way, when I got a new rear propshaft made (out of an Austin Gypsy front shaft obtained from Aylesbury's scrap yard) some years ago, I had this done by Recoprop in Luton, whom I recommend. They also took the solid front shaft in to check the balance - with some misgivings because of its apparent age, and only because I assured them I had checked it in the lathe and there was minimal runout.
On returning the whole lot to me: new rear shaft, centre bearing and front shaft:they showed me the tiny balance weight they had had to add, and said they were astonished at the quality of this original '20's part.