Arrangement for a motor vehicle comprising a first structural part of a structure of a motor vehicle, constituting a dashboard cross-member of the vehicle, a second structural part of said structure, constituting a front foot lining of the vehicle, and at least one attaching device designed to attach the first structural part on the second structural part, the device comprising: - a reinforcement element, in particular in the form of an angle iron, which is designed to be attached on the second part, in particular by welding; - a first positioning element, which is connected to the reinforcement element, and is designed to cooperate with a second positioning element which is integral with the first part, such as to make the first part occupy a determined position relative to the second part; - an attaching element which is designed to immobilize the first part in said determined position, the connection between the first positioning element and the reinforcement element comprising a position-regulating mechanism which is configured such as to vary between a state of release, in which the position of the first positioning element relative to the reinforcement element is adjustable, and a blocking state in which the first positioning element is fixed relative to the reinforcement element the first positioning element being configured such as to cooperate with the second positioning element by reciprocal engagement according to a first direction, which in particular is designed to be oriented according to a longitudinal direction of the structure of the motor vehicle, the regulating mechanism providing a possibility of clearance of the first positioning element relative to the reinforcement element in at least a second direction which is different from the first direction, and in particular is included on a plane perpendicular to the first direction, thus making it possible to compensate for alignment defects perpendicularly to the first direction, between the first and second positioning elements (14, 15), at the moment of said reciprocal engagement, characterized in that the first positioning element comprises a centering control system which projects from a first side of a wall of the reinforcement element, and is configured such as to be able to cooperate by engagement according to the first direction in a centering orifice corresponding to the second positioning element, and in that the regulating mechanism comprises an element for retention of the centering control system on the reinforcement element, the retention element being fitted such as to float relative to the reinforcement element, being the retention element constituted by a nut engaged with a male threaded part of the centering control system, the nut being disposed in a receipt seat which has dimensions, on a plane parallel to said wall of the reinforcement element, such that the retention element can be displaced according to a determined course, in the receipt seat, according to at least one direction included on this plane. - a reinforcement element, in particular in the form of an angle iron, which is designed to be attached on the second part, in particular by welding; - a first positioning element, which is connected to the reinforcement element, and is designed to cooperate with a second positioning element which is integral with the first part, such as to make the first part occupy a determined position relative to the second part; - an attaching element which is designed to immobilize the first part in said determined position,