They should bolt up to the stock engine mounts without a problem. Just make sure you have them on the correct side. The stock Matrix mounts are off-set. If you don't have the mounts on the right way your clutch bell and spur gear will not line up properly.

Another engine you might consider is the Go Tech line of 21s. I would recommend the 3 port R Spec or the 7 port with a 2047 or 086 pipe.