+100. Unless the frame has tremendous sentimental value, you will spend far more time and money putting it into usable shape than by buying a new frame.

You will have to have all of the braze-ons and the drive side dropout replaced by a frame maker and a complete repaint. There are clamp-on cable guides and "claw-mount" rear derailleurs but, if you want a reliable touring frame, they are kludges at best.

Also, I wonder how much damage your cousin did to the frame tubes when he ground off the original fittings.

Finally, yes, French and Swill threading are the same except for directionality of the fixed cup threads. Both are obsolete these days. That said, a new frame will be English threaded and replacement bottom brackets will be available everywhere.

My recommendation; hang this frame on the wall as a decorator and memento and get something new to ride.