Do you have loops for the breeching straps on the shafts?
I have seen the holdback loops in some very odd locations on those metal carts. If you don't have loops where you need them, you can take the cart to a welder. He can add some loops in the correct places, remove the others. Make the new loops open, easy to get a strap thru.
I can't really think of a use for welded on loops in the forward part of the shafts. If I can't use them, I would have them removed. Shaft tips should be even with point of shoulder of the animal in a correctly fitted cart, so no chance of shaft end falling out of the tug loops. Marathon cart short shafts have a quick release tug loop that locks thru a holder loop on shaft end, so shaft ends can't fall out of the tug loops.