And could you perhaps link some photographs of what sort of details to look for?
A good start is to look for Campag. ends... or failing that, some other similar forged(?) ends with the name of a component manufacturer on them- Simplex, Zeus, Shimano, Suntour, Gipiemme.. but usually Campag. Just about any european lightweight steel road bike with any pretensions to 'quality' built between the mid 60s and the mid 80s will have 'em.
Also, apart from the lugless, or really fancy lugged frames which may be beyond your budget unless you get lucky, amost any good lightweight steel bike in that time period will have Prugnat pointed lugs, or something very similar. The lugs on the BSA you linked to are stylistically similar, but much clumsier. Just before Prugnat, and somewhat overlapping timewise, the quality lug of choice was Nervex, as mentioned. A more ornate lug than the Prugnat. If the lugs have been worked on- thinned down, etc., then that means that somebody spent a lot of time on the frame beyond the bare minimum. Somebody cared, and care usually means quality. If you can recognise Campag. ends, and Nervex or Prugnat lugs, then that will be a quality frame built with good tubing.
Of course there are exceptions to these 'rules', great frames have been built with none of these features. Conversely, it is even possible that somebody built piss-poor gaspipe frames with Campag. ends and Nervex lugs, but I doubt it..
Very enlightening, thanks!
This may require viewing for a greater appreciation - or of course some close clear photographs - and then some enquiries here.
It's all becoming more clear and transparent.
I could and probably would considerably up my budget - I just wanted to keep it down if it were Frame Only
- as parts end up costing way beyond the price of a complete bicycle.
To be honest, 4 or 5 hundred quid depending would be within budget for a complete bike.
I've realised Racers are a different breed entirely than the MTB's I'm used to, and much more beautiful (classic bikes or classic traditional styled rather than ugly new eye sores with MTB type top tubes, over sized alloy and graphite tubing - sure they're light and fast but fugly)