Just a tip - as you've removed the arch liner to investigate (as I found out recently one exactly the same on my old girl, sorry to say my rust wasn't as bad so can offer no further advice than you have already been given, 100 per side sounds good - just
try and watch them if you can. I had a 'good job' done on enthusiastic recommendation of a family member, it was only me being pedantic that upon getting the car back I chipped away at some of the red lead paint to discover the fresh metal had
surface rust on it, that they'd just
painted over, must've taken all night / a couple of days being left bare steel to get like that, if the rate of discs rusting is a measure. I digress...)
The easiest way I've found to get them little clips is to pop the header tank off a scrap Omega (it's a single clip you ping out, then push the tank towards the right. Takes all of two seconds) then you can feel under the arch, push the central rod out, catch it in your hand, then nab the clip too, should you wish. All the others are a bit inaccessible, but the header tank one is very easy. Before you know it you'll have a good few spares. Also the arch liner isn't going to fall off if a couple of them are missing, there's them plastic nuts as well that hold it on.
