Mark it up to experience and move on is the best advise i can give.
luckily I was fairly young when I realised people where just using me to get things done for free. Since then I've only worked on my own projects and I've been happier doing it
One way to help prevent further cracking on cast iron is to drill a small hole at the end of the crack before repairing.
Also do not grind away the weld, it removes most of the material and strength
Another consideration is to match the size of the throttles to the intake, which is something I got wrong when moving from carbs to ITB's.
The throttle plate should be no bigger than the intake port (32mm iirc on the cg13)
ITB's produce little vacuum "load" at idle and quickly experience full load, when the throttle is opened, the alpha-n takes a TPS map and a MAP map and blends them together to create a better low down drive and then performance at the mid to top of the rev range