Like all rear engined cars, (VW Beetle, Skoda 100 Series, Hillman Imp , etc ), the weight distribution was predominantly over the rear wheels. gave marvellous traction in snow, but the steering got very light, sometimes to the point of non existence!
The risk with any swing axle rear was that if you lifted off in a corner, you would either make an unwanted visit to the scenery, or turn over, as the outer wheel dug in. (Triumph Heralds, and Spitfires being front engined, but swing rear axle were also prone to this.
The R8 and R10 had much better road holding, possibly due to better weight distribution.
The odd thing about the 850 cc R4 was that the engine rotated in the opposite direction to that in the 1100 cc R6TL, although the R6 used the R4 engine. The Fiat 600 and 850 were like this also, in having engines rotating in opposite directions!.
Presumably the fibre idler gears were used, as in the Ford Taunus V4, for noise reduction, but sadly, not for reliability!
Howard