Seems like if you mimic the original support,you'll have a little different buckling load as compared to the original pin location since most of the trailer weight is now ahead of the castor pin.
If you really slam it,the spring will bottom,the bump-stop will carry the load through the castoring pin,lifting the frame,and loading the air shocks.
As the rotation point is moved aft,any maximum vertical displacement at the wheel will be reduced at the air shocks since the moment arm is now longer.
The pin may tend to rotate and deform the angle iron frame in the instant before the trailer lifts.
You don't carry a lot of load in there,so maybe it's already adequate.
You do need to create a 'bumper' to protect the exposed wheel,as it's now 'outside' the protection of the frame perimeter.
"One test is worth a thousand expert opinions." Tex Johnson,Boeing
