I've just looked at this thread after quite a long absence, so my comments are a bit late, but.....
As some of you know, I had the misfortune to be in the stove enamelling business from the early '70's until the late '90's. I painted a lot of bike frames.
I guess when you ask for 'thin' paint, you are saying you don't want powder coat. Powder was unheard of when I started, but I think it has now almost completely replaced wet paint (stove enamel) Powder is much easier to apply than wet paint - in fact it is a classic example of de-skilling. It's quite time consuming to get the knack of using stoving paint, and stoving lacquer is particularly difficult, especially when you're putting it over transfers (decals).
Powder is efficient and needs almost no skill to apply, but it's always going to look 'puddingy'
compared with well applied wet paint. Obviously, the old paintwork that people want to replicate was stove enamel.
A further note on lacquering: Traditionally lacquer was applied over the transfers to seal and protect them, but when I was in this game I would often be presented with ancient transfers which were a treasured possession of the frame's owner. However, the owner rarely had he faintest idea of how they should be applied - and there are quite a few different methods. In addition some transfers will take stoving (not that hot -120C) and others will not. Of course if a transfer is 30+ years old it may behave differently from when it was young. I just mention these things to give an idea of the problems.
Double Gear Levers
Cyclists' obsessions vary from time to time. When derailleurs were young there was a feeling that the pressure exerted by the chain tensioning spring caused significant drag (not a ridiculous idea, as anyone who has ridden fixed will confirm).
It was noted that while chain tension was important at certain times (e.g. rapid descents), it was not necessary at other times (e.g. climbing). So some gears allowed for slackening the tension at the will of the rider - Huret and Simplex had gears with this feature. So I suggest the primary purpose of the second lever was for chain tensioning. Strangely most of the pros in the '50's seemed to have been happy with rod changers at the front - they knew the system worked and generally there was only three teeth difference between the rings, so they weren't asking a lot from the changer.
In conclusion I'd like to mention that I rode the Kent CA 12 as recently as 2012 using a Simplex rod changer (don't ask me why, I have no answer), and although it worked perfectly I had some difficulty in reaching it during the last couple of hours.