Car engines bolt right in. Boat engines need to be aligned with drive . On a TRS the alignment is made to the bellhousing on Transom assembly. A special tool tool with a donut looking piece is needed to check or set. It is easier to pull engine with trannie, Merc trannie is a similar procedure as BW just no rear mounts. Pull drive, loosen output bearing retainer disconnect engine and pull as an assembly. Hopefully you have engine plate mounts. If you have adjustable mounts do NOT change adjustment. Power steering has to hoses attaching to steering on transom. Simply disconnect those two hoses with a line wrench.
I don't have time to explain all the reasons why not to leave trannie in. It may come out easy enough but you will torment yourself trying to install and there is no way to check alignment with drive on. A mis aligned engine will eat parts, trannie included.