I have 75lbs. weights on mine, and just use two bolts. The weights will stay centered in the rim. I suggest bolting the inside one to the rim, and the outside weight to the inside one with shorter bolts in the two holes you didn't use. That way you can take one set off if you want. Also, that way, you don't have to fight twice as much weight when getting them lined up and bolted on.
Note: I didn't want to fight a loose bolt, so I welded a nut to the inside of my rim. Then, I just hold the weight in place with my knee and thread a long bolt in from the outside. Cordless impact and done!