Re: outboard engine weight and removal
I do not know the weight of your engine, however I am sure that any rental engine hoist would be enough to lift it off.
The most basic rundown I can give you on the transom is still pretty involved. You need to remove the old transom. This can be done by removing the inner skin of the transom and peeling it from the outer skin. You can also get to it through the top and chisel, drill or even chain saw it out between the inner and outer skins leaving a slot.
If you remove the inner skin you will need to build a new transom out of marine ply. Coat it with resin to seal it. Bond it to the outer skin using resin and fiberglass with clamps, then fiberglass a new inner skin.
If you use the slot method the easiest way to replace it is with a product called Seacast. (do a search, they have video on the process)
Which method you use is going to depend how far you want to go with the job. I have no personal experience with Seacast. Many folks have used it in here with good results. Given that my boat needed new stringers and a deck to go along with the transom, wood is my preferred method.
If your boat is solid and the transom is its only issue Seacast may be the way to go. If you are going to need further structural work, I recommend going with wood. Either method is allot of work and takes a commitment to get it done. A pro can get it done in a week or two, a do-it-yoursefer (like me) will take considerably longer. Do thorough research before deciding to take on the task.