I replaced the
axle on my 4500, but it was a little different than your Jubilee. It was a couple of years ago, and my memory is not great, so I don't have all of the details, and I think I just recently threw out all of the paperwork...
I'm pretty sure I used my angle grinder to cut off the old
axle and grind down to a usable surface.
Then I purchased a replacement
axle from a local spring & axle supplier (I'm pretty sure it was Standen's here in Edmonton). They had a great order form for torsion bar axles.
It was probably no the smartest move, but I then bolted the new axle to the frame.
And I did it all without taking the tub off the frame...
Wish I had pics, but I just took the trailer back out to the storage yard yeaterday...
Curt