Seems to me that when he said he has a '98 F150, 4.2L, 2WD that should have narrowed it down to at least a Ford product...the under-hood diagrams sometimes don't survive. After a collision the body shop replaced the metal/plastic but not the decal on my stepdaughter's truck... and I am looking for one too. The diagrams in Haynes/Chilton are so generic they are useless.
I don't have any specifics for you, because I have a straight 6-- but I'd suggest a subscription to alldata-- http://www.alldatadiy.com. It is $24.95 for a full year for the 1st subscription, $14.95 for any additional-- and they have all the diagrams/etc, all for your specific year and engine setup not like the hayne's manual.
I would help him if I could. I don't know anything about vacuum schematics though. I'd suggest trying to find a sticker under the hood of a 98 f150 w/ the 4.2L in a salvage yard. That's the best I can do.
The two elbows that connect to the PCV valve were my problem. They caused my vacuum leaks. One is under the throttle body and the other is at the back of the intake on the passenger side. I'll post pics later.