There appears to be another bolt hole below the bolt that’s holding the alternator bracket. Does it have or need a short bolt similar to the two bolts on the opposite side of engine? Also, if you are sure the timing cover seal was leaking, I read that on older bbc engines , guys were drilling dowl holes in cover out slightly. Then install timing cover with bolts loose, install balancer, then tighten timing cover bolts. Helps make certain seal is evenly centered on balancer. Also , in conjunction with that, some were installing a ready or speedy sleeve on balancer to slightly increase tension on lip of seal. One last thing, are you certain of the capacity of your oil pan? That it’s not being over filled. Some of those 396 pans were only 4 qt capacity. Good luck with it, you’ll find the solution eventually.
1966 C-10 Short Stepside HiPo Step-by-step ~ and on-going resto build in the Project Journals
