How to maximize chances of lateraling into finance from law school

For background, I am a grad of HYP, recently accepted to two of the top three law schools. I'm planning to start next year, by which point I will have spent a year working at a financial litigation boutique firm. I've always been pretty set on law school because I wanted to work in particular fields in government, but after various internships and experiences in my current job, I learned (1) those positions sucks, and (2) I really enjoy finance far more than I thought. I know that I will still definitely be attending Harvard or Stanford LS, but I wanted to ask what can I start doing now to maximize my chances of being able to lateral in to finance as early as possible? Assume I can get into a Vault 10 law firm, and I wouldn't mind working there for a few years (but I do not want to be there forever, God knows).

I know there is info about how to (attempt) to make the transition to finance as a lawyer out there, but I'm specifically looking for info about the steps I can take before, during, and immediately after law school to be as competitive an applicant as possible as early as possible. I've asked my friend's at BBs, but they are only familiar with the undergrad intern->analyst route. And to obviate comments about how my best bet would be to forget law school and focus on applying to business school, let me just say that I don't think I have a winning narrative for business school right now or in the foreseeable future, and I don't think I could get into a sufficiently high caliber business school that would allow me to 'rebrand' myself successfully.

A possible back door to biz school is a JD/MBA (I'd apply as a 1L), but I've heard that pursuing a JD/MBA probably wouldn't be worth it. But surely it can't hurt to cross-register for HBS/SBS classes when the time comes, right?

And which practice areas in firms are most conducive to lateral transfers? I've heard M&A, can anyone elaborate or discuss other areas?

Additionally, at which firms is it easiest to make the transition? Here I get a lot of conflicting info, as the best firms in general don't seem to be the best for lateraling. Also, some like Cravath are hellscapes.