In theory you can use the wires for the stock boost solenoid for the Mac valve but in fact (and I didn't install my Link) I have the optional extra loom for my boost, air temp meter and GM MAP sensor.
If you go to the Link website
http://www.linkecu.com/
you will find pinouts for your ecu although if you didn't install it you may not know which inputs/outputs have been used and which are free.