I think you've found a rare thing in Pathfinder - a way to stack four effects that all affect the same thing, even two different multipliers applying at full effect instead of additive. Too bad it's not a generally-combat-useful thing, but creative players and non-combat solutions are scary with the kinds of lifting power this will give you.
Muleback cords say the wearer treats their Strength as 8 higher for determining carrying capacity - this isn't a bonus of any sort, this is the same as actually having 8 more Str.
Enlarge person doesn't directly buff carry-cap; it's a buff to size category, which incidentally happens to double carry-cap. This isn't a carry-cap buff for stacking, it's your new (temporary) base carry-cap. It also comes with a +2 size bonus to Str, which is nice for your purposes.
Bull's strength is a +4 enhancement bonus to Str. Nothing else in this set grants an enhancement bonus to Str, not even the muleback cords (which require bull's strength to create but don't work the same way), so it stacks fine with everything else.
Finally, ant haul takes your current carry-cap and triples it. This is the only direct buff to your carry-cap you've got in the set.
So to calculate your final carry-cap, you add +8 (effective) +2 (size) and +4 (enhancement) to your Str for a total +14 and look it up on the chart, then apply the correct multiplier from size (which is no change if you were enlarged from Small to Medium or x2 if you went from Medium to Large) to find your current base carrying capacity. Then triple it for the ant haul effect.
Human 10 Str normally maxes at 100 lbs. With all four effects, they'll max at 4,200 lbs.
Halfling 8 Str maxes out at 60 lbs. Buffed, their max load is 1,560 lbs.
Half-orc 20 Str has an impressive starting 400 lbs. With all these buffs, they can carry at a heavy load 16,800 lbs, or nearly 8 and 1/2 tons.
Don't forget all these weights are for maximum supported in backpack or lifted overhead and walked with nearly normally. You can get twice that off the ground and barely stagger around with it, or push or drag five times those numbers along the ground. Yeah, the 20 Str Medium character with those buff could push 84,000 lbs (42 tons) along the ground, twice that under "favorable conditions". Have fun breaking the game, hero.