the stroker kit is exspensive, because you need to do a lot of machine work. they start with the ML320 sleeve and piston kit, which brings you up to 3.7L, this is the easy part.
Then you need to have the stock crank offset ground, and then new connecting rods installed, only to gain .1L extra, not worth the trouble. but it does make torque at the cost of less rpm. Then they install the higher lift cams.

The ML320 makes another 35hp over the stock 320 motor, and the cams might produce 15hp, then you retune the ecu for the extra 19hp, now your at 69hp. not bad but it's cheaper to do it yourself and forget the offset grinding step.