So as it turns out the KAT is only good for a template..
made up a new set of booms out of 3mm sheet and welded them up.
I have predrilled the pivot points but will make up some brass bushes and stainless shafts.
This isn't turning out to be a ten minute job.
a little CAT code paint make it look better
add one new boom set up and a new steel bucket.
and the 4200's new look
cheers andy