Clearly Marked Honda CB350/250HM344 Taken from the 1972 Honda that is pictured. Its connection to the header pipe is clean. It's internal baffle is intact. However, it is a real shame that the very end of this muffler is rotted off because the rest of it is high chrome and outstanding. The total length of a stock CB350 OEM Muffler is 27" However only the first 21" of this one are good and solid, beyond it is gone.
If you are a welder possibly it is repairable to its normal length or you could make it a shorty.