The difference in handling will really tell in the quality of tire you're buying.
If you get the 'el cheapo Pep Boys 205-75 intended for grandma's Buick that cost you $99 for 4, then you get what you pay for and handling will be horrid.
If you step up a little to a "plus" size, such as a 215-70 or a 225-70, from a quality manufacturer in a performance tire line, then you will have more rubber on the road and with the lower aspect ratio, a stiffer sidewall that will give you a crisper steering response and better braking.
You can fit many different size tires on a 7" rim. 215-70 and 225-70 fit very well. 225 may be a bit tall for a 67. Be sure to compare the tire specs between manufacturers. Tires can vary as much as an inch in some measurements, even with the same P-metric size rating.
You can also fit a 245-60 if you feel the need for alot of tire.
Goto www.tirerack.com and search by tire size, then hit the "specs" button and compare, you'll be astonished at the differences.
I do not know how you have the suspension set up but typically the higher the sidewall (i.e., the 75 vice 70) the greater the flex in corners. So usually the lower the sidewall the better she feels in the twisties...