your nissan central locking box which is a box under the steering wheel, will have two yellow wires coming out of it, one to each door. if these are cut the doors open and if you connect them to ground the doors will close. or the other way around its a long time since i did this.
i think it was:
but this was when i first got the car maybe 5 years ago, so i really don't remember. I think there was a guy advertising on ebay too, he said he had the Viewt roof patterns, which is the same as the march.
i have a couple of these cabriolets so let me know if you have any questions, they have some strange differences.
for the roof, i believe (it was a while ago) there was a company in Surrey that quoted £500 fitted for a new cabriolet roof, and they had the designs already from a previous customer.
the march cab doors are a regular k11 door that has had some bits chopped out and some bits welded in. i took some photos of the naked door and you can see where the original door ends.
if it needs lots of welding then its not worth it, i picked up a spare cab for £300, lots of rust but it...