Uprated BC box/IB5 is a lot less hassle but still need to do some chopping to the inner wings.
Fiesta centre do a five-speed conversion kit which comes with the plate to box to the inner wing you have to cut and a new tie bar which clears the box. You still need an Mk1 XR2 or Mk1 1300 smaller driveshaft and gearbox carrier. Not the hardest conversion but it isn't simple and does need some welding/fabrication.