The reason why I did this was firstly because I bought the Shimano Zee derailleur with 10sp cassette and could not return it items, and because my understanding for cycling gear was, zero to none. Since my last mini tour to Denmark left me with a numb hand for about 3 months and two very sore shoulders for about a month, I would not want to tour that would leave me in this condition. So I decided to change my straigthbar for a drop bar, I got my hands on the 3T ergonova but was left with the problem of brifters. With multiple hours of search on the web, I came across Gevenalle, a manufacture that specialises in crossbike equipment, the products and idea that they do is quite awesome, but with me being a cheapskate I could simply not afford their products. What they simply(relative terms) did was they mounted downtube shifters on to brake levers, connected with a CNC machined aluminium bracket, anyway check them out from this link Gevenalle.
Another thing worth mentioning is that Zee derailleur has a 1:1 gear change ratio, in further research I found out that that Sram force doubletap controls brifters and the Sram rival doubletap controls brifters has this as well, but the price tag is of course way, way more that the Gavenalle solution.
Which leads me to the current situation(at the time), I still had to find brake levers that could accommodate some downtube shifters, THAT could go along with the Zee. Many more hours of searching the web, I came across mods after mods, then finally I found the shifters that I was looking for it was of course the Sram 500 TT 10 Sp. It had a 1:1 shifting ratio that, with out knowing if it would work or not, I thought that I would give it a try. I bought it used for £45 on eBay, as soon as it arrived I had to try it, to my surprise, it worked! No mod no nothing, just slapped it on and a bit of adjustments here and there, great success.
On to finding the right brakes, in my research I soon found out that Gevenalle used Tektro RL520* brakes, for me it did not seem super ergonomic(on the hood) so I went and got the RL340(Ribblecycle) instead. And instead of making my own CNC machined aluminium bracket, I modified and TIG welded on the existing TT housing on to the brake levers.
Further more I wanted to have the TT500 be changed into friction, because I thought that the indexing was a bit stiff, and I found this guy on the net called nothinglabs. What he had done was 3D printing parts that would enable this function, if you would like this, visit his website, he explains everything quite well. And now after a couple of month later I can say that it works, but by no meas perfect. The problem is that the shifters has to be tighten to a certain point so it does not spring back in place, this is caused by the tension of the derailleur when it goes into lower gears. If tighten to much, the gear change is so stiff that you cant even shift it, if to loose it just springs back to higher gears, so you have to find the right spot and from time to time readjust the tightness of the shifter, so I switched it back to indexing, and it works just fine, but I’ll keep the bridges as a backup, if anyone out there wants to try this, visit his site on Nothinglabs.
All of this was done over a long time, though with all this experience, I properly would want to make my own aluminium bracket to mount on the shifters to the brake levers. And the cost of all this was £10(brake levers) £45(TT500 shifter eBay). Whether it is worth it or not, only time will tell.
*Links that confirms this research