I might go for a 3-point rig for the bridle.  From your description above I assume you plan to lift with a single line to provide the actual lifting force.  Attachments could go to the port and starboard side of the mast partner - either wrapped around it and tied (be sure lines can't slide towards the center), or use eye bolts instead of the quick-knob bolt system that came with the kit to attach the partner, then attach the bridle to the eye bolts.  The eye bolts would be always ready for use - I installed my partner with eye bolts and use them only to provide an additional tie-point for whatever I tie to the boat.  Then an attachment point at the transom - somewhere near the sculling notch as you suggest.  I drilled a hole on the port and starboard side of my transom and put a loop of rope there, simply to form a "handle" that I use whenever I need to "handle" the boat back there.  Such a rig could form a good attachment point for the one lifting bridle line that you run to the stern.

The length of the 3 legs of the bridle would need to be adjusted and come to a "point" such that when lifted they'd form a sort of shallow 3-sided pyramid over the boat, such that when pulled up the top point was a couple of feet higher than the gunwales.  The higher this point is above the gunwales, the less tension you have on the bridle lines, but the higher crane arm height you need to accomplish your lift.  You'd tie these 3 legs of the bridle together at a shackle or ring, and to that ring/shackle you'd attach the lifting line.  You'd want this ring to end up over the centerline of the boat, and over the fore/aft center of gravity.

I think this arrangement will be supportive and strong enough to lift the boat, and not damage the boat.  Remember that if you lift with only a single line attached to the bridle as I'm describing the boat will still be able to spin.  If you want to avoid that you need two lifting lines, or some guy lines.

As a counter argument to everything I said, the most supportive method of lifting will be with two straps run under the hull, one near the forward 1/3 of the boat, the other near the after 1/3.  The hull is probably shaped (thin-fat-thin) enough that straps of a proper length will not slide towards amidships, and you could still lift with one line.  The weight of the boat isn't enough that you'd need to worry about a spreader for the straps (above the gunwales) to prevent compression on the hull.  When you lift big boats the staps have spreaders.

In all cases watch that the hight of your lifting "crane" arm is high enough that the bottom of the boat comes up as high as you need by the time your bridle attachment point becomes "two-blocked" with the pully (or whatever) is at the top of the crane arm.

Interested to hear what you come up with and how it works for you.

   I have an electric hoist on roller track .my solution was to make the middle bench  seat removable and run a strap under the  bulkhead. A 20 pound weight towards the bow levels it out

   Not an NE Dory, but I did fashion a lifting harness for my Tenderly.  When I first built the dinghy, I lived on a trawler that had a davit (single arm) and a winch.  The folks at CLC suggested through eye bolts with backing plates if I wanted to add permanent lifting points, but in the end I went with a low tech solution similar to what bubblehead describes in his counter argument-- two straps run under the hull, one near the forward 1/3 of the boat, the other near the after 1/3.  I took two dock lines and tied a bowline in each end.  Each line ran under the boat and then I clipped the knots to a carabiner (two carabiners, one for each line).  I then clipped the two carabiners to the hook of the davit/winch cable, centered over the midpoint of the boat.  It proved plenty stable to lift the boat onto its cradle on the cabin roof.  As to your concern about it being hard to place from in the water, it was surprisingly easy.  Just take a bowline knot in each hand, flip the line over the bow, and then pull towards you like stepping over a jump rope.