The fillet-brazed ones were REALLY heavy. Super thick hi-tensile 1000-series stove/water-pipe steel. One-piece crank means you won't any inexpensive upgrade options. So don't plan on throwing any more money at it. I'm not sure on the exact year & models, but many from that era came with QR hubs, but in SAE axle-threading. So modern wheels with metric axles won't fit without filing the slots in the dropouts wider.