John,
I can't comment much on the Fed airbag wheel, but I assume that the mounting boss is the same as the UK version.
Also, I assume that the diameter is the same as the UK one.
If these assumptions are correct (LGM or someone else will hopefully either confirm or shoot me down in flames!), then it should be quite straightforward.
First thing to consider is your safety whilst doing the swap - Airbags can be dangerous if 'fired' accidentally - please take great care when removing the wheel.
Once the wheel is off, on the UK version there are no airbags, so removal is straightforward (1 x 3/4" nut, then use a puller to free the wheel from the shaft. DO NOT HIT IT WITH A BIG (or little) HAMMER.
This can damage the 'colapsable' shaft.
The actual steering boss is attached to the Elan wheel with a colapsable spacer piece. 4 bolts on the boss, 6 on the wheel. The spacer is threaded to accept the bolts, and they are standard M6 thread.
On the Elise wheel, the Elan boss bolts directly to the wheel with 4 bolts, going from the back of the boss, through the wheel, into the spacer boss (or just use nuts if you want to!).
Either way, you will need to get some bolts which are 5-6mm longer than the ones in the car to allow for the thickness of the Elise steering wheel.
Upon re-assembly, remember to run a length of cable from the horn push to one of the bolts to complete the earth side of the switch.
The whole job took me just under an hour, and i'm sure i could do another one in half the time now i know how it all goes.
As for driving, it is a bit heavier, but still easily manageable (even for Angie!!!).
The shape of the rim gives a better 'feel' (only my opinion - can't be based on fact).
Most importantly, there is more thigh/leg room.
It does restrict the view of the tacho guage a bit, but not drastically so.
Remember, it is only about an inch smaller, but every inch (apparently

) makes a BIG difference.
I first saw the conversion on pics of LGM's car and liked it, then when Neil did his, followed by Paul Watkins, i jumped on the bandwagon (having had a drive of Pauls first!).
After a couple of days you just get used to the smaller size and it makes for a more 'direct' steering action.
Of course - the Fed car could be totally different..........
