classic motorcycle forum

Broadly speaking, I'd agree with that, and there are some excellent Loctite products now.
My personal rule is not to modify major irreplaceable parts unless absolutely unavoidable, so I would never pop-mark loose shafts or braze on gears etc, but tinning a loose bush is perfectly acceptable as it's quick and easily replaced at a later date and does no harm in use.
Bodgers (either through lack of money or skill or both!) have always been around, even more so when our old bikes were just a method of getting to work, but I would never class the ancient engineering practice of tinning in that class..

You can buy oversize bushes for when the crank is reground. It used to be Triumph standard practice that the two big-ends and the crank nose were all reground at the same time, but things change over time.
Tinning the bush sounds good, but there are some excellent Loctite prodicts now for just this purpose, and there's no reason why the oil 'ole should get plugged when you do it either.

Don't get the woodruff key bit, though. Do you mean the half-moon tab + self-tapper used to secure the bush?

This new piece you fitted, did the welder just butt-weld it or did you slug it first?
It if was only butt-welded I think I would have preferred the flattened original for strength.

Anyhoo, as regards the B40 it really depends on your finances and the use you're going to put the bike to. Just for putting around and/or your not loaded with spare cash...keep it as is.
Competition work/concours resto/you've got too much cash...repair it.
Personally, as the tube isn't flattened, I'd leave it, but that's me.
Patina'd resto's are all the fashion now....

You asked-

Does anyone know the whereabouts of a 1953 T100C? Only 1000 built!!

to which I answered "yes"
because I do.

Isn't that the answer you wanted, or were you asking about one particular T100C? Not much info to go on if you were....

Best advice would be to get the Rupert Ratio book on BSA singles. It's the Bible for these bikes. You could use the BSA Service Sheets and a parts book too while you're ordering....
My advice would be to get it running to see if you like it before chucking money at restoring it. I had a B40 Star, and didn't really like it although it handled well.
Not a popular or sought-after bike, it must be said.

I'll second that.....good blokes, Armours.

1956 (Aug 55)  and engine number 70930, but I bet there's engines after that still with white metal bearings.