273 vs 318

I will never part with the original engine and/or parts. If I stay with the 273,the cam I select will also have to work should I decide to put the top end of the motor back to original(2barrel and all). Besides, I want to run 87 octane gas in it. I want something that is fun to drive,and can be driven anywhere. I will DRIVE it once or twice a summer to the dragstrip just for fun, but I don't plan on overdoing it. Right now,I figure that the money I was going to spend on the drivetrain can now be spent on body work and other things. No matter which engine I choose(both are in the same shape), I will probably end up putting rings,bearings, oil pump,etc. in there since the motor will be out of the car.