1998 Disco 1 167k miles
Starter heat shield was loose when I purchased the truck for 1000$
Replaced head gaskets and am now getting around to attaching shield (after welding up the mounting section).
I've tried install from above and below but it appears my options are:
Remove o2 sensor (tight as a SOB)
disconnect cat pipe from exhaust manifold
disconnect exhaust manifold from head
leave it off..how critical is it? Starter and solenoid are pretty far from the exhaust
Any inspiration?

 

You can reach it from the front. It is not that critical, but it is better to have it than not.

 

The heat shield is important .Just bought my 2004 Discovery this year- Just was stranded at Home Depot last night - Bad Starter- Starter looked new- Heat fried this starter.
Forget the metal shield . I just am putting on some Starter Heat Shield Wrap Reflective Mylar from ebay 20 bucks- Same thing happened to my old 924 Porsche- Some guy ripped of the shield before me and my starter fried- That is why it is on as an original part.
Don't cheat yourself and get stranded-