Going to take my 2007 SD into the shop, just wondering what I'm looking at in labour time. I don't have a garage nor the time to tear into myself.
Pretty sure it has a bent shifter fork or the like, as it pops out of gear under hard acceleration in fourth, and spins up like it's in neutral. Nearly pitched me over the bars last time out at the track ...
Any thoughts how long a shop would take to diagnose and fix, approximately?

It isn't going to be cheap as it's engine out and split the cases. You could save yourself a lot of the labour by taking the engine out and dropping it off at the shop and then bolting it back in again yourself. If you're mechanically minded you could take both cylinders off as well to save more labour. You've been a bit unlucky here, although the gearboxes are a bit agricultural they don't tend to go wrong.

+1 Klinck is right!

What I would do first is inspect the screen filter and see if there are any nasties in there. Also check the oil jet to see if it isn't blocked.
Not much goes wrong with these gearboxes so it is worth having a look at these two things yourself first to make sure they are OK.
It will give you some insight in what might be wrong and also peace of mind as worst that could happen is that you get it fixed and it is still starved of oil.