Engine: Not all Sierras were fitted with the Pinto engine. The later ones were fitted with the CVH engine, most of which were the 1.8 models. Also the later 2.0 models were fitted with the DHOC engine, the cylinder head is very broad and doesn't lend itself to fitting under the bonnet of a CAT.

Gearbox: Later model Sierras moved onto use the MT75 gearbox in place of the Type-9. The MT75 box is broader and wouldn't fit in the tunnel of a CAT.

Suspension: The Sierra Estate has a different rear suspension set up to give a low load area to the boot, this wouldn't fit a CAT.

Steering: Some Sierras were fitted with adjustable steering columns. I don't know if these can be fitted to a CAT but it may cause complications.

Brakes: The front brake discs on the 1.6 Sierras are not vented, where as the 1.8 and 2.0 models are. The rear brakes on the 1.6 have smaller and lighter drums than the 1.8 and 2.0 models. Some models also have rear discs in place of drums. It's possible to use any combination but the best is probably a vented disc set up at the front and smaller drums at the back. A CAT is getting on for half the weight of the original Sierra so stopping with the original brakes shouldn't be a problem. It may be worth avoiding the rear disc versions as getting a calliper operated handbrake to work well is always a hassle.

Don't forget the brake compensator is needed from the donor vehicle.

Heater: Polo Mk II heater is needed, I've found these to be as common as rocking horse sh&t in the local breakers yard. I have heard of people using a Mini heater or going for the electrical fan option instead.

Wiper: The Mini wiper system is used, again, Minis don't seem to be piled high in any yards near me.

Washer bottle: Anything than suits… Escort Mk III looks good, not too big with simple lugs to attach it with.

Tiger Donor Pack: I went for the convenience of the Tiger donor pack. This is a little bit pot luck (or some might say Russian roulette). The bits I got from Tiger were generally pretty reasonable. Although I wish I'd inspected the steering lock a bit more carefully before taking it home from Tiger. For me, it worked out OK as I didn't have a dead Sierra stuck on my drive with the hassle of getting rid of it. However, this means that its extremely difficult to get an age related plate (if that's what you want). Another disadvantage of the Donor Pack is that you don't get the little odds and sods that you might need. Its handy to have the original bolts, even if you don't use them again, as it takes the guess work out of selecting the correct new bolt.