The cost these days to get your engine rebuilt and running 400 bhp will not be cheap. Are you thinking of doing it yourself or getting a Ford Specialist to do it?
The unknown factor until your engine is stripped is what exactly is wrong with it
On top of possibly new big ends, mains, crank re-grind, re-bore and new pistons you will need a bigger turbo,uprated cams,uprated injectors,3 bar map sensor and new performance chip for the ecu and a live mapping session. This is the minimum but there are lots of other things that can be done as well depending how deep your pockets are....... uprated clutch, porting and polishing the head, wasted spark ignition,new engine wiring loom, 044 fuel pump to name a few.
Tough call for you, it depends on what you want, how much you can spend on it and how long you intend to keep it.
All I can say is you will certainly get a big grin factor every time you drive it if you go for the upgrades!!
Best of luck , keep us informed of progress.