Nice! Love the '61 Impala (learned to drive on one: 348, 3X2s, 3-speed on the column).
One bit of advice (if you haven't already), check, check, and triple check the welds where the rear, lower control arms mount to the frame. I converted that '61 Impala I learned to drive in to a 409/4-speed, and one day, while involved in a quick little stoplight battle, ripped the right lower frame mount right off the frame when I hit second gear.
We had done a frame off on that car, and everything had looked great. There was no rust, just a factory weld that hadn't penetrated like it should have.
Believe it or not, I kept the car on the road, and had it towed home where we fixed it and added a second upper link.