My truck has a bad oil pump and bearings. I bought an LS2 long block.
Can I use the LQ9 ballancer and flywheel? What other problems will I be running into?

 

I believe so, ls plateform engines are internally balanced, which allow them to interchange flywheels and balancers....i think...also what reluctor wheel is your ls2 engine 58x or 24x?

 

Your LQ9 pulley should be fine. Depending on year you'll most likely need one of these

Lingenfelter TRG-002 58x-24x Crank Sensor Trigger Conversion Module - Lingenfelter Performance

As well as to relocate your knock sensors to the side of the block. I think a timing chain cam sensor ext harness as well.