Bolt lengths depend on whether you have the cast iron or thicker aluminum water pump and what accessory brackets you have. Indeed, early timing covers had an extra bolt on the driver's side, so put a sealed setscrew in those holes if you use a later timing cover.
Since I switched to the alum wp, and my bolts were all rusty, I got all new bolts. I used stainless for the shorter ones and cadmium plated (yellow) for the longer ones where Ace didn't have stainless. The longest ones were maybe 4.5" L, but don't quote me. Some bolts go into the water jacket, some into the crankcase (oil) and I recall some are blind. I used gasket sealer on all bolt threads. Ideally, you want something that stays flexible since you will loosen some later to adjust the alternator and pwr steering pumps.
Re bolt length, best to measure the depth with a wire and write down to you insure you won't bottom out. Also, run a tap thru all the holes to clean the threads. If you missed that chance, allow 1/4" for each bolt to thread in.
