The slots probably have open areas on the back (Most I have had around, have..) so it wasn't an issue. Same goes for a lot of steel wheels, where the centers are stamped out, they end up with ridges too (how the original ones probably cleared) but the Welds or something similar might be an issue.

You "might" get lucky though and have the 5 on 4 3/4" bolt pattern on the Welds line up with the rivets so it isn't an issue but looks like they are a little close in for that off the top of my head at least.