Would you not be able to drill out the old bolt, retap or retap for helecoil for new bolt? is not the bolt a safty type feature sorta a just in case for the harmonic balancer?

 IF, tapping was possible, it should be the CRANK itself. I would not want a heli-coil. To much of a liability for me. Lots of broken parts and pieces of fiberglass scattered around would not be a pretty sight.  Just my .02

Just for knowledge sake, is that bolt real important for the balancer? did not earlier years not have them. I agree I would not want that to come off 

The bolt is a necessity on a 350, fer sher. The older small blocks(283s & early, small journal 327s) did NOT have that bolt, but they also did not have the harmonics that the 350 has, and the balancers were smaller...and fit tighter on the crank. Also, most of the older engines without the crank threaded for a bolt didn't have all of the accessories running off the front of the engine, such as P/S, A/C, AIR pumps, and all that kinda crap. If the crank has threads for a bolt, then it should have the bolt.
I don't know about using a Heli-Coil in the crank...I don't think I've ever heard of anyone doing it, but it may be possible. I wouldn't have an issue doing it, nor would I worry about it coming apart any more that I do a "normal" threaded crank. I think if I was gonna do it, I would want the crank out, and have a machine shop install it, so I would know for sure the threads were straight in the crank, and not off a wee bit....which they would be if I drilled it in the car!
Adams' Apple2011-02-16 21:00:34

Thanks thought it would be that way, I was asking because my 55 chev truck with 283 did not have the bolt, did not know when and why the bolt was added. Thought it would make good conversation. somewhere in the history one probably came off and hence the bolt was added

I think that bolt is in there fer good.  It's just too hard and even if it wasn't it's virtually impossible to get the drill straight and on center.  Think I'll start a new thread about engine options.  Must be a sign......

Hold the phone superman! I know a machinist that makes a jig that guides a drill bit dead center and saves the thread..I will try and get a hold of him so he can make one for you! Unless you really want to replace the motor because of one bolt?
Rich