NOT the same size as the 85/95HP engines. The correct nuts were cadmium plated, 3/8" - 24, 13/32" in height x 35/64" across flats.
Flat washers were utilized on aluminum heads only.
thanks kube; ive got all these engines in pole barn...frozen in right now.cant get to them i was o going to get bulk supply of nuts for model a and v8/60 and 21 stud motor....cheaper.! very helpful....again thanks...kev