Is this something that is very difficult. I can't see it being harder tha putting a car or motorcycle engine in. Also, does Merc, Johnson, etc. have different hole patterns that they use to mount the motors to the transom? I'd be looking to switch out a late 60's Merc with a late 60's Johnson. If this is a difficult task that should be left to teh true experts, what type of costs is involved? Thanks