Your are in uncharted water fixing the frame. I have a track car that we bonded a steel cage to and it had minor frame dmage that did not involve suspension pickup points and, given the added strenght of the 8-point cage, I made the decision that I'd simply re-bond the suspect area and call it good. I'd never fix a road car this way and you are nutty to take any chances fixing a suspension pickup point on a road car. Save the money you would have spent fixing the car and buy a solid, unwrecked, car.
I understand this response, the car is being sold with a new chassis. I'm questioning this because it would be silly to start to tear apart a car before trying to fix the old chassis. I've read the 'Kiss off the K wall at Laguna' thread (along with some others on LT) and it looks like my situation. From what I gather there, it is possible to purchase chassis members without buying the tub. It might even be possible to buy stock 6063 and design the part myself (I have software through work).
I am also looking into structural aluminum adhesives. My brother in law is an airline pilot and knows a few mechanics that repair aluminum members on aircraft. They seem to think this should not be a problem. 3M makes some decent products and Partite (sp?) also does some good things with aluminum bonding. The only difference from factory is cure time (no oven use for home purchased adhesives).
About the pickup point, I really don't think it is deal off. I've worked as a design engineer for formula cars, we've done a lot worse than rebuild an upper a arm mount - hell, we've rebuilt whole a-arms bent from wall loving. The majority of the load is taken by the suspension 'tower'. I can't imagine fixing a pivot point to be a serious issue. Cornering loads would be my biggest concern. However, the extrusion on there now is no bigger than 1/4" thick. If it can be replaced and secured, I have no worries with it. Although, please, please correct me if you believe otherwise. I'm not one to say I know best, I'm just trying to collect some information here.
Thanks for the info guys:UK: