what is your intention with the ancient relic?
you realize you bought a boat with a motor/drive combo that is more obsolete than OMC. there is near zero parts availability
being that old, I guarantee that since the boat is shot, you could simply cut the boat away from the motor and drive so you can take them to the salvage yard.
unless your intention is to spend $10k-$14k rebuilding the boat
$3000 hull restoration
$3000 interior restoration
$4000 buying complete used mercruiser or volvo motor and long-tail.....
.....or spend $8k rebuilding the motor and drive you have
BTW, if you started with a boat say only 20-25 years old, it would have cost you the same amount of money to buy and would save you from spending the $4k on a different motor/drive