Heloo Hans
P5 Rostyles fit straight on to the P6. You just need the correct wheel nuts. BUT, they do not look the same as P6 Rostyles. Once you have seen P6 ones - the centre on these is very domed, sticks out in the middle - the P5 ones never look quite right. They are much flatter in the centre, and they sit well out in the wheel arches.
For tyres you can use 195/ 70 X 15, which gives the same overall diameter as the standard tyres. These do get very close to the D post, but all cars I've seen them on to date have got away without needing the scissor jack mod!
Chris