I had the same issue last weekend, I too had pulled my balencer off to notice "hmm theres no damn bolt" SO I went to the local junkyard and got one from a old smallblock 350 or 400, it fits fine. but I learned a old trick for the balancer, DONT beat it , you could warp it if it is the old rubber lined one.. BOIL it in hot water, the metal expands and makes it easier to fit into the keyway., when you get it on as far as the ol arms will allow, install your bolt and washer from the junkyard. then snug it up the rest of the way. taking note to brace the engine somewhere to keep the crank from turning while you tighten. this will pull the balancer on straight and true...