Training for butterfly, esp. 200m

Hi all, I'm looking for advice on training for the butterfly. In the way of background I'm 40, male, and started swimming with a Masters swim group last summer and have been learning butterfly. I was only a fitness swimmer before last summer, and only off and on. I did a 50m fly in 35.97 last November but haven't gone below 36s since. I've swum the 100 fly four times and have done 1:31.5 +/- 0.5s each time. I would like to work up to the 200m fly but am not sure how to go about it, unlike the other strokes I can't go further simply by going slower! At this point 100m is pretty much my limit, and I only do 100m in meets not as part of workout sets. I found an article on the H2ouston site on training for 200m fly, which brings up another issue: short axis pulsing/body dolphining. First, I'm not very good at it, I spent an hour on the weekend swimming back and forth across the width of the pool (6 lanes, not sure the distance), and I can do a width of the pool underwater but I'm pretty slow. Second, I don't really understand the relationship between body dolphins with one kick per cycle and butterfly with two kicks per cycle. The H2ouston article said there would be a separate article explaining this but I couldn't find it. I've got the total immersion butterfly/*** stroke video, but so far my butterfly is nowhere near "virtually effortless" as they describe in the video. I think I have the timing of the two kicks down ok, but I'm missing the connection between the body dolphins and the full stroke, other than initiating the launch kick of the full stroke in my upper body rather than just using my legs. I also worry that body dolphins involve a larger undulation than is desirable in the full stroke. I've seen a video of me swimming fly and it looks like it is in slow motion! My impression is that I might need less undulation in order to increase turnover? I am also unsure of what extent one has to swim fly to train for fly, we don't get a lot of fly, and really nothing over 50m of fly in our workouts, and if I tried to do 100m fly in the "choice" sets I would probably have a coronary! My current hypothesis is that technique is a greater obstacle to getting to the 200m fly than conditioning so all my freestyle training is going to have minimal impact. I just have to figure that those of you talking about doing 1650 of fly or 10 x 200m fly sets must be doing something different, I can't imagine that conditioning alone would allow me to keep up my stoke for 10 x 200m! But is there some particular aspect of technique one should adjust for longer distances? Help!