Can you send us a picture of the current brushroll you have?
Your description of the DC66 brush bar part explained the situation already. There are two versions of the DC66 Vacuum, one needs short tabs and one needs long. I dunno why Dyson didn't further differentiate those two models into like.. DC66A and DC66B or something, I imagine half the people who order this part get the wrong one not realizing there are indeed more than one version of the DC66.