There are other things you can do besides swap crankshafts...
But before you can turn your mild bunny into a raging beast you need to beef up everything behind the engine too, too much power will blow the tranny up, twist your drive line into a pretzel, or at the very least break the u-joints. Then there are also the issues with upgrading the brakes to handle the new found horse power.
Just putting dual exhaust on will work wonders and wake up even the tamest V8 engine, there are also headers, alternate cam shafts (i.e. an RV cam (lots of torque)), high performance aluminum intakes and carbs, you probably already have an HEI distributor, but there are even upgrades for that.
Something else that will do wonders is to get all the $#!^ out of your car, all that weight from everything dumped in the back seat and stuff that has been in the trunk for months is added weight that makes the engine work harder and sends your gas mileage downhill. I'm not saying your car is like this but I have been people's who are.