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

I have no more info on the lugs im afraid, but my dropouts are stamped with the brand 'rider' the tubing is ORIA ML 25.

Rider are belgian but probably built in the netherlands. Could be the same builder... Or not.

Thanks for the info! I think I just found the shop its been built at (probably has changed owner once or twice), and I've sent them mail. See what happens!