Actually there are small differences in size of prism housings of various models as can be seen from table listing dimensions of various models. I did handle the 6x30 model ( and deeply regret not buying them too!). The were slightly smaller.
The 7x35 model's prism housing is similar in size and shape to comparable 7x35 one piece (B body) glasses of the same vintage. The major differentiation is in the top flange. The Ashahi Marine's flange is somewhat larger and held in place by six screws. See the attached comparison with a pair of Bushnell Featherlight 7x35 IF glasses. The Bushnell's prism housing is almost identical to the Asahi's but the top flange is fastened with only two screws and the eyepiece itself.