regardless of the age of the model, the LC4 620 SM, has smaller wheels, shorter forks, rear suspension is different. The sprockets are the cheapest part if you go to 16/45 which is most practical and may need to be changed anyway.

well if you can find all the bits and find spare dosh...
it is possible to turn a SM in to a Adventure, or look around and get a ready made one...
If you can find a LC4 SC, SXC or Enduro as I did, you got the better base to start with, the suspension is longer already but need 4.6N/mm in the front and 70/260 at the bag, a big tank and off you go, forget the wind shield, use the SC lamp mask to safe on weight... well the seat need to match the tank remember that.

here in Germany you can get a original KTM 2000 ADV LC4 620 below 2000-Euro and up to 3000-Euro fully kitted ready to roll and get it registered in Ireland, which is easy, MOT, insurance and post office... and you are set.

I just recently changed the fuel tank from 18lt to the 28lt Adventure tank incl. the vacuum pump and a seat, on my LC4 640 Enduro but have a harder rear spring already fitted, the front springs want to be upgraded soon from STD 4.2N/mm to 4.6N/nm from the Adventure, quit a lot of work at the end to study all the parts books.

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The trouble is that he was talking in philosophy, but they were listening in gibberish.