I'm nothing more than an observer from 40 years ago and somewhat hazy at that
I have already posted that the speedwell frame that the OP has looks very nice and indeed if possible I would like to buy it.
However, back in the 70's there were a number of pressures on bike shops...........the government turning off the electric notwithstanding.
We had to make a profit so things had to turn over, so in respect of frames that meant known manufacturers. Again, I remember the rep saying that it had to be joined in a special atmosphere, Argon rings a bell but that again is my memory..
Speedwell had to compete with Raleigh, Carlton, Mercian, Woodrup, Shorter, Bob Jackson, Aende, Ken Bird, Condor, Harry Quinn........the list is endless.
Then there was Trusty / Vicount and the aerospace angle.
Can you see my perspective on something different ?