tha "exact" number from tha service manual is 17.5 ft. lbs... we didn't use a torque wrench on those much anyway... no ona shop.. jus been at it with tha 2.0, 2.4, 2.5 V6 merc from 1976 to 'bout 2008... mostly hot rods.
send me an email addy and i'll send ya an oem manual (pdf) that will cover ya.............