Worth it to build my 273?

If you build a 273 the same way you'd build a 360, the 273 will not make as much power. If you build a 273 to take advantage of its strengths, (lighter components so it's easier to spin faster, smaller size makes it easier to build adequate heads, smaller bore and closed chamber heads that are less prone to detonation) it'll still make less torque, but HP may be closer.

Now if you build the whole car with the above in mind it is possible to achieve near the same or even better track performance, but the car will not be nearly as pleasant to drive on the street and your attention to details must be spot on.