When to Weld in Frame connectors

Generally the rule is to wait until all the weight is supported/bolted into the car and the total weight of the car is supported by the 4 tires and is level before welding in the connectors. Your engine and tranny are rubber mounted so they shouldn't add a twisting moment. If you're planning to put the stripped frame/body on a rotiserrie and get everything aligned, straight then I've know guys welding in the connectors while its still in the jig.