The stock immobilizer that Morgan offers for their build looks to be OK. I've got one and it does work. I've never worried about parking it and walking away. I do, however, remove anything I don't want to walk without me. The removable steering wheel is a non-issue as a great majority of people are completely unaware that they can be removed!
As for actually stealing the car another issue comes into play more and more; the young up and comings don't know how to drive stick... grin
In the grand majority of cases where I parked it and I was able to just watch what others do, it is very interesting. Most are just curious. There is a great deal of respect for this car on the order of 'look but don't touch'.
The other aspect of this is that they are so rare. They stick out like a sore thumb. They are highly attractive in that people notice them. Steal this puppy and people are going to notice and take note of it driving by.