The balancer bolt on the 305 I just put in my 79 C10 had evidently been stripped or broken off before I got it--it had a 1/2 inch course thread bolt in it,so someone must have tapped it out oversize(stock bolt is 7/16-20 thread).They had a cheap grade 2 bolt in it,and it only went in about 3 or 4 threads,and was pretty sloppy,so I found a grade 8 bolt a little longer and cut it down so it would engage as many threads as possible before bottoming out--it fit much tighter,and I felt that if it had no problems the way it was,I should not have any either.Another post on here recently had the same dilema as you,I mentioned that some mechanics feel the damper bolt isnt really mandatory,as the early small blocks (283,327)never even had a hole for a bolt in the crank and they had no trouble--his machine shop agreed,said they use locktite to help hold it on,they have done it before with no issues.
I saw one motor while shopping for one at the boneyard that had a broken balancer bolt--and a big blob of 6011 arc welding rod on the crank snout drooling over the balancer--geuss that guy wanted to be sure his balancer didnt EVER fall off! /forums/images/graemlins/eek.gif /forums/images/graemlins/eek.gif /forums/images/graemlins/screwy.gif