There are several companies rebuilding the factory harmonic dampers. I’ve used Damper Doctor with great success but check out some of the other rebuilders if they are close to you or come highly recommended. The factory damper is adequate for stock compression ratios and cubic inches but for any increases in compression ratios or serious performance usage, then power gains as well as increased bearing life will be realized using an aftermarket damper. Here are some past threads regarding dampers.

http://forums.y-blocksforever.com/FindPost38818.aspx

http://forums.y-blocksforever.com/FindPost28356.aspx

http://forums.y-blocksforever.com/FindPost19528.aspx

http://forums.y-blocksforever.com/FindPost76055.aspx

http://forums.y-blocksforever.com/FindPost1484.aspx