I've pulled the 327 from my 1968 C3 to replace core plugs.  Went to pull off the Harmonic Balancer to replace seals on the timing cover and noticed there is no bolt holding the HB onto the crankshaft.  I've heard some engines are like that but am wondering if the 327 5.3L is one of them.  This is the original engine.  It looks like there are threads in the crankshaft but I'm not positive yet.  THANKS! 

Low HP 327 cranks did NOT have drilled/tapped holes for the damper. The higher HP cranks did. Bolting the damper on started with the high horse 327s. The dampers would walk forward at high RPMs, so GM started drilling, tapping, and installing bolts with washers to retain the dampers. Non drilled cranks can be drilled, and tapped, if needed. 

I have a 250hp and 275hp 327's. Both have tapped cranks but did not come from the factory with the bolt. I went ahead and installed the bolt for peace of mind.