The problem with aftermarket dampers is the bore size. The hole size has to be very exact to yield a press fit that allows the damper to be pressed all the way on and still have the negative clearance required to transfer harmonics from the crankshaft to the inertia ring on the damper. Most of the aftermarket junk I have seen is too large or too small to fit the crank diameter properly.

I recommend you opt for a rebuilt OEM damper. It was originally pressed onto a Chevy crank at the factory and so you know the dimensions are correct. Damper Doctor disassembles the units and hydraulically presses new elastometic material between the hub and ring, while clocking them properly so that the TDC notch is actually at TDC #1.
Damper Doctor Online - Your source for Harmonic Balancers, Motor Mounts, & Drive Shaft Supports