There may be little twist to your question. It depends if the c/s is marked by the old seal. If the engine is a total rebuild,it is not an issue .
You don't want the new seal to be positioned exactly where the old one was(and was leaking).The new seal needs an unworn,smooth c/s surface to seal on.
Then there is the sealant/no sealant issue.The latest PU seal is no+sealant.
JFP is the expert on this whole subject.
Research diy,PVC coupling for inserting the seal if your fabrication skills are very good ?
Per JFP.Get the correct 5/6 speed tool!
http://www.clutchtools.com/index.php?productID=40066
http://www.clutchtools.com/index.php?productID=40065