Finally found time to get the digger back in the workshop. Made up a little jig to hold the mag drill on the dipper. Cleaned out the ragged hole left by the carbide burr with a 38mm cutter in the mag drill. Just kissed the bush, no damage to the cutter done. Wish I'd thought of that before starting with the carbide burr!!
Welded a bit of square bar into the bush and welded a bead around. Hammered out no problem.
Tapped the new bushes in until they were going straight and then used a bit of M20 threaded bar to pull them home. Turns out a standard form M20 washer is the perfect fit for a 30mm bush. New seals pushed in by hand but stayed in place, not ideal but good enough.
On fitting the hitch I managed to squeeze in two thin (i.e worn) 0.5mm shims - one each side. Hopefully they will stop the same thing happening again.
Thanks for all the help and ideas
Sam