It's hard to say since 40's are getting to be so old and somewhat rare. Those who build them pretty much fab them up themselves. You would have to look at how many people would actually be interested in this. Since you would have different drivetrains to work around I think a kit would be kind of tough to develope. I could see a 3 link kit for a 80 series being more of a popular product than something for a 40. I'm linking my 40 and even if there was a kit I would still do my own link system just because of custom wheel base and so many factors that a kit couldn't address unless each kit was custom made to customer requests but then its not really a kit anymore.