my zetec turbo mondeo used to regularly crunch diffs in its mtx75 at 275-300bhp, i dont know who told you 350bhp. and its doubtful a 1.8 on TB's would be running 350bhp anyway unless its got alot of nitrous.

regular harsh launches at the pod will knack a diff, careful driving on the standard open diff can be done to make it last.

if you didnt launch it you would get away with the standard diff, but the amount of torque steer you will get means you really need a lsd anyway because it will be a bitch to drive and pretty dangerous imo. i know mine was dangerous to drive until i got the lsd and a fairly sorted suspension package.

for some reason the st200 mondeo gearboxes are more prone to diff failure than in lower range mondeo's, presumably because they have slightly different innards and longer final drive

oh and dont use a diesel box, the mondeo 1.8TD gearbox had awful ratios and tops out at around 4500rpm

i *think* the 1.6 zetec gearbox has shorter ratio's (it says they do in the mondeo haynes) so would be better for acceleration than the 2.0 box.