Try having a look at some of the old options catalogues to get some ideas.
https://accessories.volvocars.com/Le...R_GB_NL_DE.pdf
Personally, I think Aries or Sirius wheels would look good on a 740 saloon but it's all down to personal taste.
I've always loved the styling of the early 700 series cars and wouldn't spoil the look by tacking bits on the outside. Sounds as though it might benefit from a bit of a focus on the inside.