Early-Late Harmonic Balancer question.

I have a 1963 318 Poly. I think that I have a harmonic balancer issue. The early poly engines have the timing mark on the passenger side of the engine, like the early 273/318/340. And the later LA small blocks have the timing mark on the drivers side.
Does anyone know if these timing marks were spaced 90 degree apart ? Also my engine is stock. I see that Dorman sells a replacement Harmonic Balancer for 1972 and up 318s. Has anyone use a auto parts replacement Balancer ? any issues ? I really have no need for a high dollar performance balancer.