David,

I had a conversation with the guy at this site:
http://kalimbas.com/drums.htm. Basically he said you need to
chisel/sand off little bits at a time from the hinge end of the tonge
to lower the note. Then, if you go to far, take a little off the other
end. You do this with the bottom off, so it's sand/chisel, flip over,
play, flip over, sand/chisel, and so on. Tedious. The top and sides
must be glued very tight, this is essential. Also, I read somewhere
else it is a good idea to double the width of the ends. I just glued
up the top last night, so I will make my first attempt at tuning
tonight. I'll let you know if I find anything. If you want to
converse off line about this you can email me at ryan at jimryan dot
com.

-jtpr