Unless you're going to run 5 spoke magnesium replicas or e50 rim halves with mesh centers, don't even try it as they'll look pretty crappy. The only ones that don't have some BBS type feel, and contribute to the overall feeling of the car. These cars weren't made to be ghetto blasters, if you go 19's do no more than 17" fronts, otherwise you're asking for something that unless highly specialized will look like crap.
If you try to modernize with such a large size it won't look as it should because new cars are much larger...these cars are so small. To each his own but coming from a project that was supposed to "update" the car to modern standards etc. lead me on a path to realizing what works on these cars, and its 17" fronts and 19" rears, max.
Sidewall is needed for these cars, rubber band tires don't look right...I tried a few rear tires before I found something that worked...here were the 355/25/19's
And with the right size tire 345/35/19 with a bit of sidewall so they look as they should
Here's 19's on the rear of my K3
Here they are with the 935/76 bodywork
And on a stock K3 (5 spoke mags)