Can you help to identify these frames, bikes or parts?

531 frame. If it's not badged as such is there any way of telling?

I think the Sun Solo is just a generic gaspipe frame.
Best ways to quickly check are...
1) pick it up - does it way a lot or not a lot....
2) Measure seatpost size 27.0 or 27.2 - might be 531... 25.4-26.8 probably gas pipe