I'm going to look at a 85 300sd that wont start, the owner claims the mechanic said it needs a fuel pump. glow plugs were checked

I have a 83 300sd sitting in my driveway that ran without oil. engine is seized. Could the IP on that still be good? I assume they are the same.

I've never fooled with an IP before, whats involved with removing and installing an IP? how long will it take?

and how does an IP go bad anyway?