Even the later so-called low-inertia steel ones are getting harder for parts, and the quality of replica bits has been up and down. I don't like them as much as the earlier style for the reasons I repeat below . . . originally under Minto's post about 'Points, does this look right? (qv
https://www.a7a10.net/forum/index.php?topic=16251.0):
If in your travels you come across a decent brass type, of the earlier generation, I'd grab it.
They are in many people's view 'better' for four reasons:
first, the opening point and spring are the LT earth side so a kiss (of the spring blade againt the cam-ring) doesn't kill the spark;
secondly, the double spring blade of the brass types is gentler in operation than the steel equivalent;
thirdly the points gap stays in adjustment longer (as a rule) for not relying on friction on sliding bits.
Fourthly, quite often, the contacts mate a lot more squarely too.
And a fifth plus point is that you get the option of an auxiliary earth brush on the back face, which can help reduce the dimpling at the firing points of the mag that is caused on the armature drive end brass piece by return current through the main earth brush.
. . .
It's also worth knowing that if you come across a decent BTH anti-clockwise backplate off, say, a KC2, that'll work very nicely too. Main dimensions are the same, the integral keyway that sets the internal timing is in the same place and the design is better too. New complete BTH assemblies can be had (Lindsley again) - but you need a mortgage. A Bosch set will also serve and is well made - but the keyway will probably need suppressing and reforming in the right place, or the camring repositioning.
I can't think of anything that makes me think differently this evening. The thing with the brass item is the state of the pivot post for the opening point, and the hole it goes through. The original pillar was supposed to be 0.185" (memory, which can fade so don't kill me if wrong!) but they're often pretty worn. Kits usd to be available to replace them, which is a fiddly business. Haven't seen the kits for a bit, but a replacement can be made if it must be, a fraction oversize if necessary to reclaim the opening point.
Contacts can be grafted onto the fixed and opening sides if necessary too. Silver solder job. Thus rebuilt, the brass ones can have their life extended indefinitely.
So, I'd try to keep what you have. Dave Lindsley Magnetos in the UK may have some points, certainly worth asking as his stuff usually is decent.
If going 'steel', it is apparently the case that Grove Classics, the UK Velo specialists, have taken on the production and supply of parts and replica points etc. If so, and if the QC is OK, could be an OK option.
In terms of performance, the steel assemblies will often provide a snappier opening and closing of the points which is helpful at very low rpm (due to the heavier spring rate), but overall I prefer the brass version on all the counts mentioned. For what it isn't worth!
