I have one of these "stage 3" specialised bottom ends in my s2. My bro paid around £3000 for it and a few other bits. It was also supposed to have arp rod bolts, but doesnt! i am led to believe that these are a 1800 block, rods and crank with machined pistons, the problem is if you read the small print it sayd "based" on an american tall block!! Mine has been rebuilt twice now, first time after about 2k due to piston ring snaping and doubling over another and the second time it melted a piston. I am now saving for a different engine as i know this isnt going last 5 minutes again. Like you say we all live and learn.