Gday, Just wanting to know how hard it is to replace the main rear radiator hose, the 1 that runs towards the back firewall under the air box ? and what parts do I need to take off to replace it ? I've not long bought a 91 sw20 turbo hardtop & loving it.....until now lol.......thanks in advance..... 

Very easy, as soon as you take off the airbox you will be able to see both of the clamps that hold that hose on. Only issues is that you have to bleed it after.

Yep as Phiz says depending on what aircleaner setup you have.
Also get two new little O rings for the two bleed valves in the frunk as they often leak once disturbed.
Make sure to follow the correct bleeding procedure carefully.
It is quite straight forward. Just take your time trickling in the new coolant.

Check out:
https://www.mr2australia.com/mr2play/tm.aspx?m=113820

Thanks for all that, I've tried to take out the airbox, but I"m guessing the AFM meter has to come out as well ? Now I'm thinking of doing all the coolant hoses & getting the radiator pressure tested, just to stay on the safe side. I've heard of a lot of horror stories. Thanks again.