170 harmonic balancer bolt size
borrowed from slantsix.org
The crankshaft vibration dampener bolt is 3/4"-16 UNF, 2.3 inches long, with a 1.5 inches minimum length threaded area.
You will also need a thick washer, the washer is 1-15/16" x 1/4".
summitracing.com: part number DCC-5249557AB
Mopar Performance #P5249557AB - Mopar Performance Harmonic Balancer Bolts 3/4-16 x 2.250 inch (underhead)
Or just get one from an old V8.
-hope this helps ,Lawrence