You did'nt say which hull it was 16' 17' 18' 19' ?
I had a 73 19' that had a Olds built by Mondello and came off the dyno at true 500+ hp and all I could get out of it was @ 70 mph. My boat was very heavy, it had 3/4 inch plywood layup down the sides. It was a good rec. boat but was never going to set records.
If yours is about the same I would say @ 875-1000 hp to get it that fast with a whole bunch of lightening of the boat.
Good Luck with it! BK