If I may suggest, you could use a shifting system similar to the one my team used last year and probably the one we will use this year. A video of it in action can be seen here:
http://www.billfredinthenighttime.com/694.wmv
Its not as high quality as a dog shifter, but it does work, and you could build it in 4 days starting now(2 days to get parts from mcmaster, one day to machine and one day to put together.) We used a 2 inch pulley to a 4 inch pulley for low gear and a 3 inch to a 2 inch for high gear and got RPM's I believe in the range you're thinking of. I don't have my spreadsheet on me so I could be wrong. As for an actual dog shifter, i've never built one so I Can't help you there.