FFs
If you set them up right and stop dicking around with them the standard 10inch drums single cylinder (Twin acting) breaks are fine.
My completely standard 1964 2a (no servo) will lock all 4 wheels at any speed you like, ffs how much stopping power do you want.
List of things to check first before swapping bits.
1. Get all the air out (Get a ezblead kit)
2. The adjusters are set right
Get both wheels on a Axel off the ground and rotate the
wheel forward and do up the adjuster until the wheel stops, then
back off a 1/4 turn.
3. Make sure all the bits are correctly assembled (springs in the right places).
4. Make sure that there is no oil leaks on to the shoes.
5. Check that the flex pipes are not expanding.