The quickest way to remove the old subfloor was to first saw along one of the joists near the middle of the floor. I set the blade of my circular saw at a shallow depth, so that I didn't inadvertently slice through anything under the floor. (Supply pipes for the old heating system had been turned off and drained.)
The nails holding the old subfloor didn't offer much resistance to my long pry bars, and once I got an end separated from the joist, the rest of the board popped out quite easily.
Where the boards ended at a wall, removal was fast and simple. But where the boards continued under an interior wall, I made an initial cut about 6 inches from the wall, which let me quickly remove most of each board. Then using a reciprocating saw, I cut back the remaining stubs flush with the wall framing.
As you can imagine, dirt and debris from several decades had accumulated in the spaces between the joists, along with loose cellulose insulation that had been added at one point. To give me a clean starting point, I vacuumed the bays thoroughly as I tore out the old subfloor.
Keeping your balance as you walk on the edges of joists can be tricky and dangerous, so I tacked down a few of the old boards for safe footing. Because storage space in the house was at a premium, I built temporary supports out of scrap 2x4s and loaded all the LVL joist stock into the room.
It became obvious that I would need a place out of the way to position my laser at a consistent height while I installed the joists. I ended up building a small platform that I suspended from the ceiling near the middle of the room.
With the joists cut to fit just inside the exterior sheathing, it would be tough to slide them by the stools on the two windows, which faced each other from the center of opposing walls. My solution was to cut notches in the framing for the joists to slip through.