That airplane design, like some people here, is at least 62 years old. Most markets change every half century or so.
Yeah, not really on the designer, but since 2024 T3 2" .058 wall tube seems hard to find, I wonder how easy it was 62 years ago.
Interesting point is that today's 6061 T6, is most likely stronger than 2024 T3 was 60 years ago.
The recipes are the same, but the quality and purity of the compounds has much improved over the last 100 years. There is a couple of scientific references to this on the Net.
For a rudder post, I would use 6061 T6 replacement without hesitation, it is not weaker than the 2024 as an initial structure, it just has an earlier yeild point when it gets bent 'X' distance, compared to 2024's further 'Y' distance, question is, why on earth would your rudder post ever get bent that far .....