There's a shop just up the street from me that does this. Marty Burke Motorsports, aside form doing a few of my racing friends engines and other drive line components, he uses the process on his own engines. I know he has two identically C/SA engines with only difference one being completely cryogenically prepped. The cryo motor is faster. Can't explain the difference other than the cryo.
Here's a brief dicription of the process from his webpage.
www.martyburkemotorsports.com/cryoclass.htm