Renew as many of the cam-drive components that make up the assembly as possible, including guides, tensioners and chain. Also check the camshafts themselves for wear or pitting on the lobes. The camshaft gives the engine it's power and torque, a substandard cam means a substandard engine!
Interfacing new parts with old will cause the new parts to wear prematurely and lead to a less than satisfactory outcome.