Yes, you can do that. It is much easier on a trolley jack though.
Firstly, make sure you have used a clutch aligning tool, and put a little grease on the spigot bush (in the end of the crank) and on the geaerbox's thrust bearing.
Once you are ready to mate the two up, it is critical that the engine and gearbox are exactly straight, otherwise the engine will never ever go in. This means you need to drop the back of the gearbox down a long way to line up straight with the engine.
As the 2 get closer together you may be able to use a long bolt or g clamp to pull together the last bit - but again make sure it is straight, don't force it.
It is possible that the engine will foul on the engine mounts while doing this, if so remove them until the box is bolted on, then put them back in.