First of all, cool bike. I have owned a couple MB-2's and they are excellent!

Regarding your questions, most newer, indexed bar-end shifters are going to be specifically for 8, 9 or 10 speeds. Finding the right 6 speed indexed bar end shifters may be difficult and probably cost prohibitive. However, most any bar end shifters, new or old, can be set to friction which would allow you to use it with any speed, just not indexed. Hope that makes sense.

You also asked about moving the bar ends to the top of the bars. This can be done with a set of bar end shifters and some thumbies from Paul's components: http://www.paulcomp.com/thumbies.html EDIT: I see you meant brake levers. Yes, cross tops.

However, I have always preferred to simply mount mountain bike style thumb shifters on the top of my drop bars. You will have to slightly expand the clamp to fit it over the bars but they will function equally well to a Paul's thumbies, IMO.

Drop bars are indeed a matter of preference. You can typically find a used pair for cheap on craigslist. I would strongly recommend 26mm clamp diameter rather than newer 31.8 because you will need to use a 26mm quill stem on the MB-2. Again, hope that makes sense.