Re: I am a dope...
Ugrrhh, since I posted that, I though I'd figured it out from diagrams, logic and memory. You've got me doubting myself now.
Anyway, in answer to your question, removing the LPV is reasonably easy. At first glance, I didn't really fancy the job so thought about getting a well known Alfa specialist to do it. Unfortunatly when they quoted me five hours labour (to do the brake pipes also...) I fancied it even less but decided to have a crack anyway.
You really need to drop the tank to get at it, which isn't as bad as it sounds. I didn't take it all the way out, mainly because the nut on the safety plate at the top of the tank has rusted to dust, so I couldn't disconnect all the hoses. Instead I just rested it on a trolley jack and lowered and raised it as needed. (The car is on some high ramps at this point so there's plenty of room). To be perfectly honest, you might be able to get a spanner onto the bolts holding the LPV in place without lowering the tank, but mine were pretty rusty and I prefered to get a decent socket in on the action. You're gonna need more room for manouver at some point anyway. So far, I haven't seen any need in dropping the exhaust.
Other than the bolts, you've got to disconnect the brake pipes from the top of the LPV. I was replacing my pipes so I just chopped them off. Easy. Unscrewing the in unions in situ might be a bit of a struggle, they rust on pretty tight.