Jay,
I've got these on my Series II and I love them. They don't seem to come off but much care must be taken regarding parking too close to the kerb. The Australian supply comes from the US. They need to be fitted by a professional. I did drive around for a while with a broken one and the only issue was that the missing section threw the wheel out of balance. I reckon they set off the wire wheels very nicely but a few of the people who comment on the car on the street don't like them.
The fake rings do wear the tyre if not installed properly, there needs to be a small gap between the white wall and the tyre otherwise it rubs as the tyre rolls and deforms and could eventually wear through.
As for taking the engine and cross member out the bottom, do it. I was one of the people who replied and it is much simpler IMHO than taking the thing out through the top. The car had to be lifted about four feet at the front and I did it using the supplied jack, blocks of timber and a trolley jack to wheel out the engine and gearbox.
AJR