If you know the dry weight of the hull minus gear and your boat weighs hundreds of pounds more ( Taking the motor weight into consideration. ), you could have water below the deck. This could saturate the flotation foam which would make the boat perform poorly, and make it unsafe to operate.
Water below deck can also quickly start the rot process which will destroy the stringers ( They support the deck, and add structural rigidity to the hull. ), and destroy the transom ( This is where your motor hangs, and gives it it's support.) Unfortunately rot below deck can be difficult to find. The deck can seem solid, and the transom can seem to support the motor fine when in actuality you have major problems going on down deep.
A 43 year old boat unless stored in the dry year round, and well cared for all its life will likely have rot and or structural issues that will need addressed before it can be considered safe to operate.
Given the pictures you posted above a thourough investigation into the stringers and transom would be a good idea as a start. If you take core samples and find the wood to be dry and golden then you can look at the cosmetics. If the core samples show wet and dark wood then she may need a full restoration.
Go through some of the restoration threads and you will quickly see boats rot from the bottom up, and from the inside out. Fortunately there are plenty of people here who have tackled projects like yours, and lots of knowledgeable people here willing to help you get her back on the water.
Start with cleaning up the inside, and start looking for cracked or damaged fiberglass. Then post up some pics. Then you can decide on the next course of action.