Seems a wide range of HPs to be trying to estimate speed.
A 57 Viking is similar to a Starcraft Jet closed bow, i think its a 14ft. Might be a heavier gauge of aluminum and thus a heavier boat then a Starcraft
Whats the hurry. Most vintage boats are used for cruising, not speed trials...
And yep, rated for a 60hp.
IMO you and your friend would do best w a great running 1980s Johnson motor w tilt and trim, in a 50hp.