bottom end

Hello Gents, I got a situation where i need to replace my bottom end (scores on rotary valve plate) and found myself looking on ebay. My motor is a 720 silver motor (2001 GTI) and I was wondering if i could use a white 720 crank case, the only thing i noticed different was the pulse nipple...

I have a 96 gtx with the 787 engine. It ran really great untill the engine seized. I took it to a dealer and they told me that the bottom end needs rebuilt. I guess some bearing in the bottom end went bad. I have some mechanical skills and am wondering if this is a rebuild that I can do or if I...