First, can you get any information/diagrams from Shamrock assuming they offer this as an option and are still doing business? That would be my first inquiry.
Second, how's your confidence level
scary and tedious boring big holes in a finished body...measuring 5-20x, checking the angles....yada yada yada
Third, you can get a rollbar kit from either Finishline or Cobra Restorers.
Forth, you will need to have mounting points welded to your frame to accommodate the roll bar attaching points....unless they are already on your frame. They are not just a drop in and fit, the bars will probably need to be cut for height and fit for the back brace if on a 427 or even a 289 forward brace.
It can be done...I did it on my car but it took about 3 weeks of prep before I bored my first hole