RB20 altenator bolt up problems?

[90240sxca18]

I had a S2 rb20det, then got another S2 rb20det, i switched over my altenator, from the first motor to the next.. but....... The bracket where the belt tensionor bolts up to, does not match up with the bolt hole on the top of the alternator. Has anyone ever herd of this? the hole at the top of the alternator is about 1/2-3/4 an inch below the mounting point on the bracket.. im confused.