Using the original bolt to press the harmonic balancer back on is a really bad idea. Dont do it. When using the original bolt the stress is on only a few threads which can lead you to ruin your crankshaft threads.
JEGS Balancer Bolt, for Big Block Chevrolet, Grade 9 High-Tensile Alloy Steel, Includes (1) Hex Head Bolt, (1) Balancer Washer, & Lock Washer
Chevy Big Block 396-427 8 SFI Certified Harmonic Balancer
2339640 CHEVY 396, 402 & 427, 1965-1972 Mark IV, 8.00” Harmonic Damper 0-Bal - PRW Performance
65-74 Crankshaft / Harmonic Balancer Bolt Set - 396 / 427 / 454 With Washer Kit
2339640 CHEVY 396, 402 & 427, 1965-1972 Mark IV, 8.00” Harmonic Damper 0-Bal - PRW Performance
Harmonic Balancer Bolt Kit & Pulley Bolt Kit Fits Big Block Che-v-y 396 454 Engines : Automotive
Harmonic Balancer Bolt Kit & Pulley Bolt Kit Fits Big Block Che-v-y 396 454 Engines : Automotive
454 Big Block Chevy Crankshaft Pulley 2 Groove - SWP Crank
A-Team Performance Harmonic Balancer Installation Tool Compatible with SBC Small Block Chevy — Southwest Performance Parts
Other Belt Parts for 1968 Chevrolet Impala for sale
Big Block Chevy Crankshaft Pulley, 396 427 454 V-Belt - Long Water Pump : Automotive