Trying to identify my 1950s Lenton Sports

[bikeworkshop]

Great to know, thank you. So I have a 1957 Lenton Sports (which happens to be the year I was born). I'm going to enjoy restoring this one.
I already have a dilemma with wheels. Looks like the bike originally had 26x1-1/4 wheels (597) which are impossible to find. I'll need to go down to 26x1-3/8 (590) or up to 700C (622). Down feels better - at least that was a proper British size at the time. I have found a nice set of GB Coureur 66 brakes for it so I'll need to work out how far they will reach. 3.5mm shouldn't be too much to ask hopefully.

You should be able to find 26x 1&1/4 wheels - i might have some, but try the wanted section.
I would say Dunlop lightweight rims in this size are not unusual on ebay 32/40 - then build the wheels on the appropriate hubs

Likewise the tyres - once you've got a pair you might never wear them out!

650c Is very common in storage, 571etrto, popular in tt, very unfashionable now but too fancy to throw away.
Vintage look might be challenging.

650a I think might be the same etrto as 26 x 1 3/8 but narrower tyres and rims available, but easier in France, rare in the UK.

I wouldn't go for 27" wheels. I fitted some to the frame from my father's old Super Sports to build something I could use to hack to and from work back in the 80s - handling was 'unusual' to say the least.

High bb, also messes with trail? Feels horrible.

Some frames were built with the expectation that you might use either wheel size, but I think the steering geometry would need to be different.

 

[vociferous]

For what it's worth, if you do decide to go with 26x 1 3/8" (590), I have found that on a 26 x 1 3/8" Endrick (Dunlop or Sturmey) rim, the Kenda white-walls on Amazon (I can find the link for you) have a width of exactly 1 1/4" when inflated to the max. spec. of 65psi. I was pleased to find this to be so when I installed them on both my Hercules and Elswick. In contrast, my vintage British-made Michelins on my Rudge (with Westrick rims) are 1 3/8"-wide when fully inflated to 50psi.