RoyBoy, Daniel- thank you both for your replies. Re-reading the TCA Western Division website on LR http://www.tcawestern.org/lr.htm, I see that they explain the use of the rectifier, in fact they explain all of Louis Roussy's patents. The info for patent #5:
"Patent #5 was French patent FR 815 449 (A), applied for March 24, 1936 and issued April 12, 1937. This patent described and claimed a remote control method for the direction of rotation of a DC motor equipped with an inductor having a single winding consisting of making, taking into account the polarity of the supply conductors, the inversion of the field in one of the two circuits of the motor to be controlled (inductor or armature) by means of a rectifier of the type of those used for the transformation of alternating current into direct current. This was the second time that a French manufacturer of electric toy trains utilized a rectifier to remotely control the direction of travel of a locomotive. The first who tried to go in this direction was JEP (JEP patent #8 of 1935). Such a rectifier technique had already been studied in Germany by Märklin a few years earlier. According to a first embodiment of the invention, the method was applied to a 'series' motor and the rectifier was then located between the inductor and the armature. In a first variant, the respective provisions of the armature and the inductor relative to the rectifier were such that in the armature the current was always maintained in the same direction whereas it can be reversed in the inductor while playing on the polarity of the power source. In a second variant, the respective provisions of the armature and the inductor with respect to the rectifier could be reversed so that in the inductor the current is always maintained in the same direction whereas it can be reversed in the same direction, induced by playing on the polarity of the power source. According to a second mode, the method is applied to a motor 'bypass' and the rectifier is then located in the circuit of the inductor."
Daniel- many thanks for the offer to assist with finding parts. Interestingly, I came across an advertisement for another "Super Rapide" which also has the pilot and pony wheels missing, but the seller mentions they are common to other LR models. So far I haven't been able to figure out which models that would be, but I did find a number of photos of the complete complement of wheels (and the tender pickup) on the internet: