SM64 3DAS is NOT allowed for a 70 Star run and is a category extension. However, it IS permitted for the Mario 246. That leaves me wondering if 3DAS is allowed for SM64 during a solo any% 1545.

We generally follow the same rules as the individual multigame runs. Since 3DAS is allowed for Mario 246, I would say it's allowed for Solo Any% here as well.

One of the other mods can feel free to correct me on this if it's wrong, but I believe this to be the case.

Yes, 3DAS is allowed for this, we follow individual rules but also marathon rules, and if it's allowed for 246, then it's allowed here (one of the 1545s I did 2 years ago, I did SM64 120 on 3DAS and is on the leaderboard)