right I see your problem were the shaft bends about 1 foot from the tips.
Youll need a tug stop ill tell you how ok if you look at the shaft as if your pony was in it so the cart is levle you need to drill a hole not right through but on one side of each shaft for a 3/16 1/4 pin to be inserted.
When 3/16 1/4 diameter pin is in weld them up so the pin is tite.
The pin length sticking out of the shaft needs to b 2- 2 1/2 inchs long.
Then check if you need an extra breeching d (ring) leave the oridginal one there just add another one each side of the shaft.
And your problem will be truley solved.
I hope this helps and let us know how you get on ok.
Ps in my albums there are some diagrams which will help you understand I hope thay provide an insite as well.