OK... Ugly cranks aren't a deal breaker. Your Suntour cranks* are square-taper, so you don't necessarily have to replace the bottom bracket. However, it would be a good idea to do so since there are other issues with bottom bracket length that need to be dealt with.

Back to your original question: yes, you can replace your Suntour crank and bottom bracket with a more modern crank and BB and not change anything else. You will want to buy a road double crank with a 52 or 53 tooth large chainring, 8-speed compatible and matching English thread bottom bracket. Sell your old cranks and BB on Ebay.

*The Cannondale catalog says a 1989 SR 600 had a Shimano 105 crankset. By 1989, Suntour had all but disappeared. I think your bike is from a year or two earlier.