Yeh , the .75 has a raised area in the center big enough to drill and tap . My .46 does to but it is not big enough to drill and tap . I think it is part of the design on the casing to add strength .

I will be padding all sides of my tank now . The original design of the plane had the tank fitting through a plywood structure in the fuselage with no room for foam except in front of the tank and behind it . Since im rebuilding the whole bottom front end of the plane I will be able to make room for foam .

The pic with the big round nob in the center is the .75 the other is the .46 . I also made about 8 sets of these motor mounts outa T6061 aluminum and am going to try and implement some rubber in them like those ISO mounts you have .