The system Cthulutech uses does not lend itself to modification to other systems. There are three reasons for it:
First, and this is the one that makes it hardest, the system is based on choosing out of three different ways you can calculate your dice rolls - the highest die, adding the highest pair together, or taking the numbers that make up a straight and adding all of them together for a final total. There is a marked versatility to this that removes a lot of the bell curve normally associated with 6-sided dice rolls, since such bell curves need a straight set of d6 added together for a working bell curve.
Second, the difficulty classes for various things one does are based on this skewed system of dice rolls. The chances of successfully rolling higher means that the difficult to achieve is also markedly higher. Swithcing the systems lowers the number of ways a PC can roll their dice, because the other systems don't use multiple dice (D20) or use a different number on the die (d10's) and thus make it too easy to gain higher rolls without altering the difficulties to reflect that.
The last reason is the simplest reason: it's time consuming and fraught with the possibility of making something too hard or too easy by accident. Much easier to use the system as is than alter it on your own.
As for my two cents, I'd love to play Cthulhutech. Tentacles, Eldritch Horrors, and impossible odds abound, as well as monstersex. ^_^