Just out of curiosity

fstrnldr

Twins do not mean you have to drop the engine. It is up to the installer and often other items going in. For example a clutch install at the same time would be a good reason to drop the assembly out of the car. The other factor can be the tools at your disposal. There are some specialty tools that can make the in car install far quicker than even thinking of pulling the engine out. This would obviously make more sense for someone that does this on a daily basis rather than once or twice in a life time.