studs
Hi,
The Buick block is tapped for standard bolts. 5/16-20. I think.I view your use of the stock neprene gasket with some trepidation,as I had a leaker after several months when I replaced the rear main seal in car years ago. I am putting my motor together finally, and have purchased the thick cork gasket. I hear these can leak too,so I am going to dust the gasket on both sides with high tack gasket adhesive, see if that helps. Of course, it is important to keep the surfaces as clean as possible, and the oil pan rails should be in great shape, nice and straight. Those dimples make them hard to check, but try to use a straight edge.
If my fresh motor gets leaks, I think I will try "The Right Stuff", a super silicone that is pretty good stuff, just very pricey.
Good luck with your job!