One caution. The old letter system used for silk lines was based on line diameter, and made some assumptions about the lines tightness of weave and its consequent weight. The new system is based on weight as measured in the first so many feet of line less some measure of the front tip or something. The point is, it is based on weight. There have been many conversion charts over the years and some even agree with each other. At best they are all a good point of beginning. And then this is complicated by the nature of bamboo rods. One guy will swear a bamboo rod casts best with a 7 wt line, the next guy knows for a fact that it is a 6 wt rod. Chances are they are both right but one casts or fishes differently from the other.
Use the conversion charts as a good beginning but don't be surprised if you like the rod with a different line.
AgMD