Ikea Maximera in other cabinet; exact dimensions?
I know this is 9 months old, but thought it worth mentioning to others that might find it, because the selected answer above is incorrect.

The "frame width" that IKEA is referring to is actually the outer dimension of the IKEA frame / cabinet (Metod in Australia). The cabinets are 18mm thick, leaving an internal width of 364mm.
That is precisely the width of the Maximera drawer.

Since your internal width is 395mm, (31mm wider), you should use a timber strip / moulding of 16mm on either side. 1mm difference won't matter.

I just fitted 80x60 maximera drawers to an 80cm custom cabinet (slightly oversized at 82cm). I used 67x11mm mouldings either side and it's perfect.