At the weekend i was strenghting my rear traling arms,i wondered how you took the shocks out,i only undid the lower mountings,and you were right Steve by the time you cut out for the lower shock mount its not worth the mod
As you worked out, Dave, you can strengthen the corner where they normally break (if they are going to anyway) but all you are doing is MOVING the point of least resistance forward to a point just behind where the shock mounts locate!
The Carledo is still running its original 1973 trailing arms (Ziebarted from new) and despite the fact that I have 135+ bhp going through them AND a brake line lock that permits static burnouts, I've not had any problems with them! I think, personally, that corrosion is the major factor in trailing arm failure and power increase/hard usage is only a minor contributor/accelerator of failure!
As further proof, I recently replaced a broken (corroded) trailing arm on a 1980 1500HL AUTO with only 53k on the clock. You couldn't GET an easier life than that one had and still failed!