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______________
Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"