Agreed, use a block of wood, especially if you plan to jack up from either of the pans. This allows you to spread the load and significantly decreases the chance of you puncturing the pan.
Driver's side transmission mount: make sure nothing is obstructing the transmission from above. And it doesn't hurt to pop the nut off the top of the front engine mount to ensure that side has as much flexibility as it needs. Consider jacking it up from the large vertical seam along the differential (location A in your picture) and not from the transmission pan.
Front mount: remove the dogbone mount on the passenger side to make sure you have as much flexibility as you need. It might also be helpful to pop the top nuts off the driver and passenger side mounts to ensure flexibility. It doesn't need much clearance, though, but it is tricky to fanaggle out. I think I jacked this up from the inside edge of one of the pans using a block of wood that fit the entire side of the pan. This is important because it helps spread the load and takes advantage of the structural strength of the pan edges.
Passenger side mount: absolutely do not forget to remove dogbone mount first. I jacked it up from the leftmost side (er...passenger-most side, viewed from front) of the engine oil pan, using a block of wood that fit the entire side of the pan. Once again, popping the top nut off the front engine mount might give you the extra flex you need.