You probably will not be able to make both of them work together (same remote etc.) Plus you said that it did not do much any way. You will be better off to but an all in one, remote start, keyless entry and alarm, and just trash the old one. The actuators will not be to hard to install, all of the push rods in the door are easily accessed and a generic one will work fine for what you are trying to accomplish.
Zig