[DDF]

I could be wrong, but I think the reason there is no number on the frame is because that is an aftermarket or home made frame. Somebody has come up with a clever way to make an old 7x00 planter a narrow transport because that is likely necessary in Europe?

 

[DDF]

It looks like 7000 planting units so like redrivereast said, it will be from the 70's or 80's.
Nothing wrong with mechanical drive, unless you want to do variable rate.
I actually miss the simplicity of mechanical drive sometimes.
Read the seed population charts in the book, change the top and bottom sprocket, choose high or low range and away you go. On older planters like this you will want to inspect all the mechanical drive components for wear, to see how much you will need to put into it once you get it home; drive chains, sprockets, finger pick ups, etc.