Train unloading balancer

[opaque birch]

do i just use 3 to 1 balancers for each of the cargo wagons and then do a 7 to whatever i need balancer?

[terse venture]

You don't need 3-to-1 balancers on the cargo wagons, it doesn't matter if those chests are equal or not. So just a 7-2 balancer is needed here