I made the upgrade from cantilever to V type Linear pull brakes I did change my levers but you can also get some QBP Travel agents so you can use your old levers but for what they cost I bought new levers.
Why do you need to buy new bars and stem to install Linear pull brakes?
By the way upgrading the brakes made a huge difference in my stopping power it would be a highly recommended upgrade.
You can see my upgrade in some of the photos on my Tandem Project page link if you like.