If you look at the class records for the 273 stockers, compared to a 318, 360 or 340 that will give you an idea of what a difference there will be between the sizes of motors. Cubic inches x airflow x good combo x rpm = horsepower. Your 273 is hampered with a 3.31 stroke and small bore, and in need of a solid cam and better valve train,rods and pistons to build a lot of hp. It can however respond to basic stuff like headers, manifold, cam etc. Just remember you still only have 273 cubes.
There is some fun in taking the road less traveled, so you might find it a lot of fun to develop a package that will run hard with a small motor. That of course would be easier with a four speed than an auto trans.