The Stingray brochure from 2001 with a 320hp 6.2l (383) did 65mph with a 21” prop ( a good 383 should put out 475 ft lbs torque and 490 hp). So 60 hp for 5 mph is pretty accurate. Be nice to have a sleeper family boat that can do 80mph though!

Few stingrays in the microboat thread i started on speedwake many yrs ago. Was the go to internet thread for single i/o boats under 24’. Many boats listed had small blocks. Speedwake ended but Do an internet dive, you may find the thread.