First SR is NOT the same as Sun Tour - not related at all, other than they were both Japanese.

Mid level and up SR used Tange Cr-Mo tubing; #1 and #2 are double butted. The lower the number for Tange tubing, the thinner the walls. SRs are great riding bikes, and because they are not very well known, the transaction prices are really low.

SR used a mis-mash of components. There is little if any collector demand for SR bikes; thus I suggest using what ever works best for you.