Is this your first motor overhaul? If so or even with experience a good repair manual helps. Generally speaking, welding thin aluminum, unless your really experienced with the TIG process can be another heart breaker. I have done it and could do it but no longer have the HF and AC TIG welding setup.
So the piece you broke out, is there a hole behind it that supports that rod? BTW when you seek help on the internet you get advice, not the skill of the person giving the advice. Skill in being a mechanic comes from experience and making mistakes sometimes until you learn.