That saw was made in the early 80's and the case is the block. You would need to cut and grind the case down to something useable. I have done many trimmer and blower motors but there is a lot less material to remove. I have done one like yours but I used a Bridgeport mill to make nice angles and radii cuts. Looks cool too.

Try these links:

http://www.echo-usa.com/technicalresults.asp?model=601s

http://www.echo-usa.com/oot/docs/CS601SE_050275.pdf

Good luck.

Tim