Very much doubt you'll get 200bhp, you'd have to put a 16v alfa/vauxhall unit in to do that. I had a 120 multi, which had a partially gutted dpf and a remap, with a cg motorsport clutch.
I had to change the clutch disk from a kevlar to a dual friction type, as the kevlar kept slipping, even after a 1000 miles and running in.
The Dpf was partially gutted to keep the noise lower and keep back pressure up slightly to keep torque up in the mid range.
It was remapped to @150 bhp/190 lbft torque. It absolutely flew in the midrange, and would pull 110 on a steep uphill private test track and 117 gps mph on a flat private test track, not amazing but very usefull in the real world.
It did 42 mpg average, and was lovely to drive gently (most of the time) due to its generous torque curve, great fun to drive as it also handled well as you know, also fitted drilled grooved discs and ferodo pads, tbh brakes are not well specced on multis compared to newer models that stop on a sixpence.
Great fun to drive as a street sleeper, probably made lots of people take their cars back to the garage for a checkup, and had no problems overtaking cretins who accelerated when you overtook them.
The 120 multijet engine is magically a lot better than the 115jtd, might even have a slightly different turbo.
BTW havent seen those seats before, were they an option or recovered?
Good luck with the build!!