Sorry guys
I sell Stainless fastenings for car restoration and have used them all over my own mini without problem for over 10 years and have many satisfied customers. The limiting factor on the subframe mounts is the bodyshell metal. This will yeild before the bolts. I know of autotest minis using stainless bolts on the frames and altough the speed isnt high the loading is! On the subject of strength just think how easy it was to break the old bolts whilst you tried to remove them after the corrosion had set in ( and they are "plated" when new). Using a class 70 or 80 cold formed rolled thread stainless bolt will be fine - DO NOT use anything that has been turned from Hex bar or been tapped onto a blank.
There are places I wouldnt consider selling bolts for on the mini and these include Brake Calipers ( V high grade), Drive flange ( again V high grade) and Seatbelt mounts (very complex laws about head shape - you must use genuine bolts).
On a final note - there is no "perfect" bolt - everthing is a trade off, high tensile strength equals low ductility etc etc.
So no vested interest in what you say nite fire ???
