The Harmonic balancer to use with the inline six is the Innovators West part,
as it is designed for these applications.
I know this,
as the www.inlinesix.com fellows use it and it cured their harmonic problems.
They have taken this GM based engine to 9000+rpm.

They used to have cam gear drive problems etc.
Used to have balancer to crank fretting problems,
went to the Innovators part and cured that deal.

It's not built like the average balancer,
some type of internal clutches.

LHP
www.haywardperformance.com