i dont want to step on anyones toes here. Just my opinion as an installer so take this with a grain of salt. i strongly disagree with what awohar said adding the adapter makes it more sturdy than the sd mount. Not true the .4 dish like the superdish mass has it's own mass and suport arms given that both are mounted correctly and securly what ever one you add the adaptor to will now be the weaker mount. Making the neck longer think of it as a pry bar whats easier to pry something up with a shorter bar or a longer bar now think of wind being the muscles not to mention adding an adaptor can make it harder to correct plumness in the mass later on. either way my opinion is if your gonna mod your sd mount for the sake of the .4 use a pipe and self taping screws.
Or what i have done in the past and im no carpenter ,and maybe i shouldnt have done this but i was in kind of the same position customer didnt want another mass on the roof and pole was no option here. i talked him into letting me carefully pull up the foot plate of the superdish i then filled in the screw holes with pitch patch/ roof tape then applied pitch patch to the backside of the new .4 foot plate and mounted in the same spot as the old super dish sealing the holes first and then covering them with evan more tape and a whole new mount called the guy a few times from time to time never a problem. maybe this is wrong but it seemed so right lol