This distinction hasn't been drawn. Maybe it's obvious.
If the Bronco II has an FM146 or A4LD, you can remove the bellhousing while under the truck, and it's not hard to get out from underneath.
If it has a Mazda M5OD, you can't remove the bellhousing, and it's quite a lot more difficult. Though I believe you can put the transmission on the ground and jack up ONE frame rail just to get it out from underneath.
Be careful with cinder blocks. When they fail, they fail very suddenly. And they are designed to hold a uniform load, which doesn't describe your vehicle. Railroad ties will take quite a lot more deformation before failure, though if you put one under the tires, please make sure the vehicle can't roll even a tiny bit...