I've just completed some work on my 1997 TF Magna fitted with 3 litre 6G72 engine.

I replaced the valve cover gaskets and inside both heads, written with texta colour, are the letters LPG.

After cleaning the oil off the outside of the heads, stamped into the aluminium are the letters LPG.

(1) Was LPG an option in 1997 for the Magna? My searching indicates it was not sold untill 2000 in the TJ. We purchased the car with 70,000km on it, a number of years ago as as far as I know it never had any LPG gear fitted to it by the previous owner.

(2) What engine internal changes are made for the engine to run on LPG. I presume that my engine has the stamps because there are some internal differences.

Ive got the same on my tf advance. Pretty certain advance onwards had the lpg ready heads. I dont understand how it works completly, but it means that they are suitable for running on lpg without any addition.

Mine is also fitted with lpg now

Higher temp valves, possibly harder seals..
That's it.

Higher temp valves, possibly harder seals..
That's it.

I bought our 98 TF in 2000 (40000 km, ex EPA car). At the same time, I bought a new NL pajero. I phoned Mitsubishi Adelaide about them to confirm that they were suited to LPG. The guy asked me for the chassis and engine numbers, and when i gave him the details, he asked if it was an Advance model. Yes - it is. "This is indeed your lucky day sir - the Magna is 100% LPG compatible". The pajero already was (because it said so in the sales blurb.

I have since replaced the rocker cover gaskets (on the Magna) and have seen LPG written in texta on the heads. Both vehicles have done over 240000 km on gas with no troubles due to gas thusfar.

In the good (bad?) old days, of engines with cast iron heads, hardened valve seats and stellite faced valves could be inserted into the heads to make them LPG friendly.
(No, I don't know what "stellite" is either, but Wikipedia tells me it is "a cobalt-chromium alloy designed for wear resistance. It may also contain tungsten or molybdenum and a small but important amount of carbon.")

Heads had to be machined for the valve seats to be inserted because valves normally sat on the iron of the head. With alloy heads, it is just a matter of the manufacturer using the right materials for valves and valve seats.
Not sure, but I think Mitsu used hardened valve seats when leaded petrol became obsolete a long time ago and these may be ok for LPG.

In short, only valves and valve seats need to be LPG compatible.

My TH has the LPG engine as well.

When we bought our Magna, we looked at a new one, and were informed that an LPG compatible engine would cost a few hundred more than the standard one. We bought the TF Advance second hand and luckily it had an LPG compatible engine. At the time, I was advised that the difference was in the ECU, but I think that if they went to the trouble of stamping LPG on the heads and also writing LPG with Texta pen, the difference is in teh heads themselves - probably in the valve seats.

Stellite is a very hard material which, and hardened valve seats are often called "Stellite", but are not necessarily so. They may simply be hardened cast iron inserts, or maybe the cheaper engine may be the iron inserts and the LPG engines use stellite which would be dearer. Stellite can bewelded but it is very a tricky material to work with. ANy machining has to be grinding, so again it is expensive.