Geof, yes they where marginal for strength. I was heavily into motorsport at the time and fitted a formula junior spec engine. Soon got outclassed and went the Shorocks supercharger route with a 2"SU carb. Next weak link was halfshafts, cured with an Escort/Capri rear axle. Got fed up with the whole thing and swopped for a Lotus 7.
A Holbay tuned 1725cc rootes engine was far to much for a Standard 10 rear axle but fun when nothing broke. The bank of Mom put and end to playing with cars.