Wouldn't be easier for you to just order old style battery, with 2 screws instead of new with 4 screws, and somehow modify the fixation points and charging connector? If it is in stock, of course.
Where I am from, even the standard, samsung 18650 cells are cca 10€ each. So 12s*2p*10€ is 240€. Than you have to buy BCM, bulid everygin and still figure out fixation and charging connector. And you also need the charger...
I believe, this is what
@O38 did. It looks like much less hassle, than complete build. And not much more expensive.