Just thought i would add my experiences for anyone who reads this in the future, i have just changed mine recently and you do not need to remove the re-bar, you do not need to de-gas the air con (if you have it), you do not need to remove the sheer bolts on the steering column.
the process i took was,
1. disconnect negative battery on terminal
2. disconnect pipes into heater core (engine side) and drain coolant
3.remove drain gutter and windscreen wipers and motor
4.remove the 2 10mm nuts that secure the dash to the bulk head.
5. remove nuts under the 2 tabs on the heat proofing next to exhaust. (these secure heater box)
6. remove steering wheel and air bag
7. remove all switches, trim, glove box, passenger airbag,clocks, panels etc around dash
8. remove centre console (2 bolts under rear ashtray and 2 plastic bolts under gear gaiter.) you will probably need to loosen the handbrake by undoing the 2 13mm nuts
9. remove dash
10.remove white plenum in front of heater box (2 plastic nuts)
11.remove padding under air con unit to allow access and remove metal clips around connection between black heater box and air con unit. (not sure how this part goes for cars without air con)
12. remove sound proofing from above heater box area, ( 2 star shaped washer type nuts)
13. make sure all plastic heat directors are removed from heater box and slowly wiggle and pull heater box away from bulk head. (this take some force and movement, you have to be brave)
14. with a lot of effort and wiggling pull the old heater matrix out the black box. ( smashing it to pieces with a hammer will make you feel better here)
15. wipe up all the coolant at the bottom of the box
Before you put the new one in make sure you remove the plastic protector at the bottom if it has one, otherwise it will not fit back into the heater box and it could damage it. I got my heater matrix from euro car parts for £30 delivered they were cheaper than GSF.
Follow the steps in reverse order to fit the new matrix. Before you reconnect the battery put the key in the ignition and turn it on, this will make sure the airbag light doesn't stay on. Also make sure you are not inside the car when the battery is reconnected just in case the air bags go off.
Fill the car up with coolant and leave the expansion tank cap off, start the engine and let it idle for 5 minutes. Top the coolant up and screw the lid on. Let the car warm up until the fan kicks in and check for smoke from the vents and leaks into the foot wells. There will probably be a bit off smoke at the beginning form left over coolant.
In total it took me about 7 hours in a darkly lit garage. Just make sure you keep all your nuts and bolts safe in a tin or jam jar or something!!!!
I hope this will help anyone who has this problem in the future
