Well, it there are 3 buildings on the site then that eliminates the SE corner of Main and 100 S the NE corner of State and 100 S or the NE corner of State and 4th.
It could be the NW corner of State and 200 S, Carl's Jr, old beto's/eat a burger and the smoke shop or the building north of the old beto's.
It also doesn't sound like it will be on the old Zephyr corner, only one building in the way there.
I would guess that the 32 vs 42 will simply come down to how much of the corporate office they plan on bringing to Salt Lake City and how much additional space they are wanting to lease out in order to lower the overall cost of the building and being able to recoup some of the costs.
I am simply guessing but I would imagine they have a % of leasable space based on needed square footage and the more they need the more leasable space they will want to build.
I could be totally up in the night on this, I've never built my own corporate tower.