You would be looking at a fair bit of $ for the cable, brake lever and bits. Check ebay & InMotion for both and it will give you an idea of cost. Another point to consider is your shifter will not clear the case unless you mount it vertically and cut a bit out of it to shorten the throw & so you can get your boot on it more easily. Fairly awkward especially in a section, standing on one leg. If you try to mount it lower you must bend it outward to get it to clear the ignition case and the lever will be unprotected, just looking for a rock to hit. Also, I found that the kick start assembly was in the way of the lower mounting-very unsatisfactory all round. As above, the "feel" from the cable operated is spongy feeling as well.
The cap you have on the shifter shaft is likely to break apart. I found that a piece of black fuel line over the well greased splined end gave a nice look and good protection. The caps are still available but as always, for a price. It might be an idea to get an old alloy lever and cut it to fit with a spot of weld & put it on the left side, vertically and see if you like it before you invest-Good Luck, it is a nice looking bike!