Sounds like a good plan Alan but i think you may be better off lifting the engine and box out as one unit. There's only one mount at the back of the box to support it while the engine is out and the only way to remove the box separately is from underneath. It's not easy and neither is replacement.
I would suggest the following method :
Remove the bonnet. Yes i know they can be set vertical for better access but that won't work with the next step. Also remove the radiator, slam panel (or as much of it as possible from the top of the rad) and grille.
Jack the rear of the car as high as you can safely get it on axle stands. Remove the prop shaft and unbolt the gearbox rear mount.
Leaving the back end up, disconnect electrics, fuel lines etc from the engine and remove the nuts from the engine mounts.
Sling the engine and box, if necessary using a load-leveller. Roll the hoist in and lift towards the back of the engine so the engine/box combo is as near parallel to the floor as possible.
Once clear of the mounts (and all other things perhaps forgotten) roll the hoist away from the front of the car, lifting the hoist as needed so the engine/box clears the front of the car.
Once the engine is out, it will be much easier to remove the sump, head, pistons, big ends, mains etc and when refitting, to use Plastigage to confirm the new shells are the right size and/or adjust the shells. The time saving involved in doing it this way will be more than the time saved by trying to do it
in situ.
Refitting the box to the engine before refitting will also be much easier, getting the torque converter to engage in the oil pump drive in the box and turn the TC while aligning the bellhousing with the box laying on your chest isn't easy!
