OK, time for an update! Probably the only update the car will really have.
I had the Fairmont converted to LILPG this week, & I think it will be great

I opted for a cylinder tank instead of a toroidal one, and even though it's only been one day I'm very happy with how it drives so far.
Performance matches petrol except 60-80 feels a *little* slower. Purge time on cold startup is <20 seconds & half that on warm startup. The idle during purge time feels like my old wagon but then it's back to normal after that. It stalled immediately after one of the warm starts (turn key, car starts, car shuts off), but I think this was just a one-off.
The engine bay install looks great, and I'll get a cover for the tank in the boot, but my sole complaint is the gauge on the dash. It's an LED gauge with green & orange LEDs. I'll see at the 1000km run-in service if I can get another one, but to be fair to the installer I didn't ask about what kind of gauge I'd be getting, and I only decided I didn't like it when driving home at night; the green & orange clashed with the rest of the Fairmont's white/red theme. If I can get a replacement gauge with white/red LEDs I'll be 100% happy with the install.
Tank range & fuel economy readings seem a little out (6.0-7.0L/100kms seems optimistic, it was previously getting 7.0-8.0L/100kms on petrol) but this might sort itself out once the system beds in? If not, it's no biggy.
Pics to come over the weekend.