Very very difficult to tell from a photo but as no-one else has had a go ...
As you can see and touch the lamp you are in the best position to try and determine whether it is a repro or old conversion. You say it weighs 3 Kg - I expect quite a bit of that is glass shades. Does the metal work feel weighty, what is the quality of the casting? How are the electrical attachments made, what are the electrical fittings like?
If it is a repro made to be electric, then the electrical fittings should look like part of the construction, not an added after-thought. Personally I think it is quite attractive, though the inner chimney looks wrong to me - too tall, probably should only slightly protrude above the shade, and most of them seem to be clear not frosted.
As far as value is concerned, I would guess that age probably doesn't make that much difference. To an antique lamp collector (and there still are some around) its value would be reduced by the conversion. Its value is as an attractive working lamp. I don't know where you live but you may like to look for an antique lamp specialist in your area - there are still places around that sell spares and replacement parts for antique items. They would certainly know.
