When I was building up my RGS I bought some new lines, the type that look like the originals. I noticed that the bores of the actual pipes was nowhere near as big as the BSA originals. I consider that plenty of internal diameter is vital on the feed pipe in particular, as on startup it is pulling treacly 20/50 down to the engine, so I put these aside and bought some good modern stainless braid covered hose in 8 mm bore, and used that with the original end fittings. For the clamping of the hoses, I turned up some crimp outers out of aluminium alloy, slipped them over the barided hose, and squeezed them up using a 4 jaw lathe chuck, plus a second stage when I used a piece of 3 mm steel, rounded at the business end, to slide between pairs of jaws and tap with a hammer, to end up with 8 closing crimps rather than 4. May sound odd, but it is gentle, neat and it works.
I do get irritated when I buy replacements that aren't as good as stuff made 50 years ago.