The input shaft does not move fore and aft, just rotates. Stick it in fifth (or any gear really) to stop it rotating.

Make sure you have removed the gearbox top front support (the long black banana shaped one) Raise the gearbox on trolley jack. Slide engine studs into gearbox and slide back. When you hit resistance rotate the crankshaft and jiggle the engine. The input shaft splines will locate and the engine should then slide further back till it stops on the two dowel pins. Another (more forceful) wriggle to locate them. Fit the nuts on the bottom studs, and drivers side bell housing bolt in to hold it together. Remover the gearbox jack and lower the engine. You may have to push back slightly and it should just drop the engine mount studs straight into the slots in the crossmember. Ensure the engine is square (amount of slot showing on engine mount mirrors the opposite engine mount) and bolt everything back together.

Good luck

 

What him and her said^^^^, see even i'm not perfect, sometimes.