Go with It!
The car might slow down a little. The car will respond to nitrous very well if the lobe seperation is close. Other then that, when you put in the 347...make sure the compression is closer to the 11.5--12.5 to 1 area.
Other then that you might want to put on a smaller carb to pick up some bottom end response.
Those AFR 205 heads flow almost 50 cfm more, out of the box then the ported heads you just sold! If you were going to stay with a 306ci motor, I would recommend the AFR 185, but no need to spend your $$$ twice.
Good Luck and let us know how it turns out