My mate has an ARC 'cooler on his M35.
Straight swap for OE.... expensive though
There are a few kits available (in order or price) from Greddy (Spec V, Spec R), ARC and Dolphin.
There are probably more, but I cannot think of them off the top of my head.
As far as I know, the Greddy 'coolers need some cutting to fit, but the Dolphin is a slimmer design and fits without cutting (from memory).
As stated the ARC is a straight swap for the stockie.
If you don't want to spend that kind of money, I suppose you could take the dimensions of any of these and duplicate whichever you like.
Can't guarantee the custom job would cool the same though.