As to what wheels fit: There are lots of replies on this in the archives. Lug pattern is 5 lugs in a 4-1/2 inch diam circle, "5x4.5" as usually expressed.
Here's a site somebody posted a while back, that lists lug bolt patterns: http://www.streetracing.org/shop/wheelguide.html

You will see several Japanese makes that use this pattern, and many US models still do, although the metric equivalent may be designated.

You still have to check that center hole diameter is enough to fit over your hub centers, verify lug nut compatibility, and check that rim centerline offset from the mounting flange is appropriate, usually similar to original. One indirect measure of this is called the back distance or rear spacing and it is a direct dimension you measure with a straightedge and a ruler or tape. Look up the Stockton Wheel or Wheel Vintiques sites for diagrams of wheel measurements and clearances. For some sense of what tire sizes agree with what rim widths, go to tire listings in tirerack.com and see "specifications" for candidate tires. You can duct-tape some wood or cardboard "padding" onto the sides and treads of the tires you have now to simulate the proposed new ones and see where the fits might be tight. Roll the car to and fro on your driveway and steer the wheels to the limits. Bounce the car down at any tight spots, too, disconnecting the shocks if necessary to get lots of bounce.

"Handling" is not a precise term. What you have as a priority handling characteristic may differ from what I do. Good, sharp steering feel, trustworthy mountain road cornering grip both wet and dry, and reasonably quiet and non-harsh ride are what I enjoy and seek. This does not require the widest possible tires and rims. I tend to select tire sizes of the same or only a modestly higher load-carrying rating as the originals. Oversize tires eat more horsepower and 120's aren't over-endowed with hp. Modern tires are vastly better than those of the 60's and 70's, and most of your handling improvement comes from this; the rest is because you have to use wider rims due to the wider tire profiles now sold. I find that 60-series widths and lower tend to take more caster in the suspension alinement of old cars built for bias ply tires or the original 85-series radials, to restore straight-ahead tracking and avoid sideways wander. Have fun with this planning.