Daytona-Replacing Valve Springs

I apparently have a broken valve spring in my '72 Daytona. Is it feasible to replace the springs without removing the head (using compressed air to hold the valves closed)?

Of course I would need to verify no damage to valve or valve guide in some manner first.

Any recommendations of a shop in Central or Southern Calif that could do this, or the bigger job of renovating the heads?

Thanks