A useful device to have handy is a Meccano strip roller. These can be used to either straighten bent or distorted strips and plates or create a smooth curve for model building. Pictured below is a couple of Mervyn Bishop’s rollers, one narrow for perforated strips, the second wide enough to accommodate flexible plates.
Opposite is a Meccano Magazine article of 1978 dealing with construction. It is easy to adapt the plan to the Meccano you have available.