just started cleaning up the engine bay (needed it, and plan on swapping over the engine cover and front rocker cover) when i noticed this tab with LPG stamped on it.... i've owned the car since it was about 2 or 3 years old, it's never had LPG fitted? not sure if it's related or not, but the intake plenum seems to have a more shiny, almost polished finish to it?

http://i32.photobucket.com/albums/d1/asylum83/2012-01-23-175900.jpg
http://i32.photobucket.com/albums/d1/asylum83/2012-01-23-175909.jpg

More 'advance' models, and some altera's so it seems had IIRC harder valves and seats for the higher burn Temps of LPG, and the other specs and clearances remained the same however...
It's just a LPG spec head, no other changes, same block, pistons, cams etc.

Apparently the 3.0L had an 'LPG' compatible spec head on it with what SH00T says, but all 3.5L engines are compatible.

ahh ok, mine's a 3.5 Altera, so i guess that'd explain it.

what about the slightly shiny intake plenum? i'm pretty sure most other ones i've seen were a more raw grey/matte finish?

3.5 6g74 still had LPG head releases, and were stamped accordingly, mostly Advances. But not all 6g74 have been stamped..
No idea on the plenum, I'll look at my uncles 01 TJ advance with the LPG stamp next time I see it...

Pretty sure all the Advances were LPG compatible, as we're the Altera's. (The Altera & Advance that I've owned previously had LPG stamped heads). I suppose they were the only ones that would've been covered by warranty in the event of damaged heads in an LPG converted magna?

As for the manifold, neither my Altera or Advance had a manifold as shiny as yours. Perhaps it's your cleaning regime?

my TJ Series 1 Executive has LPG heads

When I bought my wife's TF 3.0L Advance, and asked about LPG compatibility. They guy at the other end of the line asked the engine number. I told him and he said it was OK. He said that all advance models were LPG cpmpatible,as were the 3.5 engines. Apparently the Advance engines had a 'A' prefix on the engine number and this is LPG compatible. I cannot verify this at present because the Magna is where it usually is - out on the road somewhere.

I'll get a photo tomorrow, but as I'm currently replacing the rocker cover gasket (and cover, to fit an engine cover) I noticed what looks to be 3.5 LPG 74 written in texta... didn't think it looked like something that would be done in manufacturing? I seriously doubt the head was replaced in the first 60,000ks?

Could that read 3.5L 6G74 ???

here 'tis
http://i32.photobucket.com/albums/d1/asylum83/2012-01-25122642.jpg

looks like

3.5
L P G 74?

As for the manifold, neither my Altera or Advance had a manifold as shiny as yours. Perhaps it's your cleaning regime?

hahahahah cleaning regime! engine bay hadn't been done in years! (although you did inspire me to go a bit nuts the last 2 days)

it seems the "shinyness" is not just on the intake manifold, looks like it goes to the lower manifold and heads....

http://i32.photobucket.com/albums/d1/asylum83/2012-01-25122747.jpg

No explanation here. Your car is just a freak.....
Custom order fallen through maybe....Hand assembled???

it did make 127kw ATW, from a pod filter and axle back exhaust? nothing extreme but not bad for almost stock