With the 4000 series you add S to the part number to get slotted, ie... DBA 42029S.
Note that the 6x6 wiper slot style 4000 series has been replaced with the new T3 style.
You may want to check that number again, the catalogue specifies 42027 for VE rear sixes, the number you have is for V8 rears.
Best have a check with Greg at GSL Rallysport (forum sponsor), he would know it down pat.
they dont come up on the DBA website, you sure about the model number?
Know what you mean mate, best off downloading the PDF catalogues on the website.