Im not the most up one MK1 fiesta's but, heres what i have to offer:

The inner wing shouldnt need cutting, 5 speed boxes are longer, i believe this is why they cut them.

Engine mount should fit, if not get a MK2 XR2 engine mount as they have CVH's.

Brake servo: If anything i would of though the master cylinder would need upgrading, the servo's are usually the same, master cylinders are usually a bigger internal diameter on larger engined models. (if its got brakes designed for an 1100 u wana be upratin the whole lot, be shit scary otherwise)

Don't think theres a lot else u seem to have listed the main problem areas