I have (had) bar-end shifters on my Semi-Pro and it was easy to accomplish the double shift. In terms of gearing my problem wasn't the lack of low gears, the 48x34 combination at 38 gear-inches is exactly the same as 39x27 on a modern setup, but the high gear. The longest I had was 54x14, which is about 50x13 on a compact crank and less than 53x13 on a regular one. It was plenty on flats and gentle declines but I spun out on anything steep.

A few years ago I was able to substitute a 6 cog cluster made by Maeda that fit the original spacing, 120 mm I believe. I had to replace the original chain with a narrower 8spd for it to work. That cluster, called the "New Winner" by Maeda, had 13-15-18-21-26-30. I appreciated the closer spacing and higher gearing to some extent but the evenly spaced double shift progression was lost and with 2 overlapping gearings I ended with 10 distinct gears anyway.

I've looked at the serial # pretty closely again I think what I thought was a Y at the end is just some errant scratches, so the number seems to be KS16148.