If you have rot in the transom, just do the whole job at once.

I used Seacast in a minor floor repair in a 1970s boat; and am quite impressed with the product; albeit I have not run the boat yet.

change the water supply hose

Take lots of pictures. .. we are simple people and like pictures. .. lol

Paint bildge with gel coat:boat:

Fix the transom now. I dont know where your located but where im at there are plenty of weekends left until boating season.

Along with all of the other suggestions...consider replacing the bilge blower and hoses. It's also a great time to add access lighting to the bilge so you can see what you re doing at night!!

It may be extreme but a co worker of mine actually installed a remote video camera in his bilge and connected it to his navigation network...very cool.

Have you sprayed gelcoat? That was my plan. I have about 25 years in auto body business, I have used gelcoat but never sprayed it. I have brushed it in to make moulds before. We have a spray gun for spray polyester which requires a 2.5 tip ,I think it will do gelcoat also.will it flow out smooth?

I have gotten some good ideas so far ! Keepem coming.I will try to get pics up soon!

Check the water hose transom fitting, sometimes they get clogged. For that matter, check all the cooling stuff. It's much easier on a stand.

Does this boat still have the factory liner in the bilge? if so your rot may have spread farther than you can see, I just went through the same issue and same boat 3 weeks ago they had installed 6x6s under the liner to support the motor and they didn't have any fiberglass covering them and the floor drains in the cockpit ran down the stringers right to them and they turned to mulch IMO id try to check those while you have your motor out... there are what look like drain holes just below the motor mounts look in those you should be able to see the supports and if they are wet or not...I found mine trying to figure out the drainage system on the boat and what I learned was there was only one and its in the far back just below the transom assembly and this is where mine rotted my transom...If you decide to run what you have I would suggest making some support for the motor I made stainless angle to cover all of the motor mount area to spread the weight out until I found the bad stuff....I decided to cut the liner out and go with a conventional stringer set up and leave the liner out... I'm starting my glassing job soon and I've gutted this same boat and am in the process of building it up now if you have any questions about it just ask these guys on here there is a ton of info and knowledge.. Good luck with the resto