I've been getting asked this a lot so I figured I would post this here and explain what is needed to retain your engine cover after the intake manifold spacer is installed.
When you receive the intake spacer, in the hardware bag there will be a small aluminum spacer with a button head bolt and washer screwed into the end. Remove the engine cover stud from the bracket at the pass. side front of the engine. Screw the stud into the spacer, then secure the spacer/stud assemble into the bracket with the supplied bolt and serrated lock washer. It should all look like the picture below:
The stud height issue is now taken care of.
To take care of the oil cap/filler height issue, you will need to order GM part number 92068813 (described as "TUBE"). It is an oil filler extension and cap from a 2008-2009 Pontiac G8 w/ a 3.6l v6 engine (NOT the v8 engine part)... It's about an $8-9 dollar part you can order at your local GM dealer, or pick it up online.
When you receive that, you can either use the oil cap that comes with it, or use your old one, that's up to you. Screw the extension into the elbow oil filler on the driver's side front of the engine. The tube extension kind of snaps, and locks onto the original, once it's installed it will be VERY DIFFICULT (Impossible?) to remove, so be warned.
Install oil cap and you're done.
That said, if you're going for all out max performance, I recommend running without the engine cover anyway. All it does is just keep the heat from escaping the intake quickly and acts as an insulator. But I suppose you can put it on for car shows, etc this way...