I understand the Panda and 500 share a platform and some mechanical parts with the Ford Ka. How much do they have in common?

What parts are interchangeable and is there any difference in price or quality between Fiat and Ford parts?
Are wheels the same PCD. I've never seen a Fiat on Ford wheels, or vice versa but if it was a straight swap these could look quite good combined with a bit of a drop, and a little different.

I ran a ka and put my punto wheels and tyres on it but the profiles were lower so the Speedo was slightly out
Wishbones looked the same but a pain to change as it needs bumper removing
Steering rack internals same but needs drumsticks changing over
Personally I found the Ford rubbish in all respects

500 and Ka back axles are identical. Ford were not happy with the ride and handling of the early 500s which is when the integral anti roll bar and softer springs came in.

I used the 500 rear road springs on my 169 Panda. It certainly gave a nicer ride but they were too short. I've not checked but suspect the Fords have a longer rear spring than the 500.

The Vauxhall Adam seems to have a lot in common with the F 500, though wikipedia says, "Adam is based on a shortened version of the Corsa D platform"

Ka is on the same floorpan as the 169 Panda/500.

The Adam has no relation to the Ka at all, apart from being a similar size.