You can drill a small hole in one of the bolts.
Or you can just leave that bolt out, but use the other three...
If you use the other three, then the lock tab for the oil drip tab may get in the way, you can then enlarge the bottom hole in the camshaft thrust plate where the tab goes and re-bend the tab so it can fit in the new hole along with the other bolt...
Some engines did not have the top bolt in the oil feed hole and just left it open and did not come with the drip tab...
I like to use the drip tab to help direct the oil on the chain better...
But you can run without the drip tab, the oil will still get on the chain from the oil slinger.
Sometimes it may be hard to drill through the center of a bolt without breaking through to one side if you don't have a lathe to make it easy...
But there are a few options. Just leave the hole open, or run a bolt with a hole drilled in it...
Here's my write up on the front end assy of a small block...
http://www.forabodiesonly.com/mopar/showthread.php?t=287231