[Dazza]

Thanks for the responses.
Rivets that I am using are AN470-6, still learning this little art, but I think this is just an issue of practice.

The major problem I am having is the 2024 bend radius wont fit the bulk heads and other brackets I have, the radius is to large which is why I believe the material used was something else. I think the 2024 that has been used in race cars in the late 60's when the cigar shape was common, the large radius' posed little problem.

It looks to me that 6061 might be the best bet, I will get small sections of the others for an experiment.
Looks like I will have some reading to do with the AC 43.13-1A and Otto69, thanks for the tip on adding the extra sheets, i have been flat out trying to work out where to get a radius bar made, great solution.
Well to continue reading all the links you guys have given, thanks again