There will be absolutely no come back on either the seller or the inspector. The absolute best you could hope for is the inspector refunding cost of report, if they so choose. I wouldn't waste any time or effort beyond a phone call stating the facts and asking if they will assist.
There is much more to the above, which some others have touched on.
You have purchased a boat which in current condition is worth maybe 3 grand, in top condition approximately 10. It is completely unrealistic to expect a 40 year old boat and 14 year old motor to be free from defects. It is even more unrealistic to expect anyone other than yourself to be liable for them when purchased privately.
If a boat without defects is expected, a new boat is required. Even new boats come with problems, but they also have warranties.
I have bought and sold many boats, always sold in much better condition than purchased. Repair costs just go with the territory of second hand boats, particularly anything over 10 years old.
I do feel for you, and have been caught out with unexpected expenses on second hand boats myself.
You could always just put some ply down over the old floor and use the boat, transoms need to be pretty bad before they are really a concern. Ofcourse if you sell the boat, i would be telling the purchaser.