High speed Alexander (?) head belt type

I have mounted my High speed head on a Promjksa Deckel clone. The motor has a four step pulley and the quill three steps,so the belt always runs a bit cockeyed. The groove shapes seem to be that of a conventional pulley drive belt. My problem is that unless the belt is really loose, the motor will not start on a static convertor. Should the belt have a round section?.
I believe that the head is an Alexander as the speed chart is in English, but there are no manufacturers logos etc, though there is a part number (?) PG 104 on the ali base casting - any suggestions?
Frank