The 8 speed tricolor should work no problems (the dura ace would require alternate calbe routing and would likely be a bit off even then). Firstly, it should have enough travel to cover the highest to lowest cog.
Secondly, as the derailleur isnt where the indexing is (thats done by the shifters) then as long as the actuation ratio (the amount of cable pulled) of the derailleur is correct then it should work just fine. With the exception of 8 speed and earlier Dura Ace all Shimano indexing derailleurs have a ratio of 1.7 (well 1.67 apparently).
For example: Shimano 8 speed derailleur, shifter and cassette. The 8 speed shifter pulls approx 2.8mm per click. Multplied by the derailleur actuation ratio of 1.7 gives 4.8mm -which is the spacing for shimano 8 speed cassettes.
Now, for 10 speed - the shimano shifters pull approx 2.3mm per click. Again, multiply this by the actuation ratio of the derailleur (the amount the derailleur will move) and we get 3.91 and the cassette spacing for 10 speed shimano is 3.95.
So, basically as long as the derailleur has enough travel (which it should - im currently using a 6 speed on my 8 speed setup - works fine!
) and the actuation ratio is the same (which unless its dura ace 8 speed or earlier it will) then you should be good to go!
Or as i prefer, try it and see!