RoLo50312

Ok, so I am really hoping someone can enlighten me. I saw a listing for an old Brooks saddle for $20 but it came with a bike I didn’t want. I figured I would take the saddle and donate the bike to the co-op. Once I had the bike I started to think that under the grime and filth it is actually kind of cool. It’s a little small for me - a 54 (I normally ride a 56). So instead of keeping the saddle and getting rid of the bike I started thinking about cleaning it up a bit and selling it - I had been thinking about $100-120 after new tubes, tires, and bar tape. I have been cleaning it and discovered the rims are true, hubs spin smoothly, canti brakes needed slight adjustment...but the down tube friction shifting is all out of whack. So then I looked closer and realized the touring triple crankset is a 48/38/18. It’s a six speed cassette 13-30. The 18T chainring appears to be affixed with some type of bright purple adapter. So I’m thinking this must be an extreme adaptation for steep climbs with a heavy load. But it seems like there is no way that all gear combinations can possibly work. Has anyone ever seen this setup? Is the intent that the rider knows that if using the 18T chainring that it will only work with the largest couple cogs in the cassette? If I shift to the 18 in front and 13 in the back the chain droops down with no tension and massive slack. The setup seems pretty odd and I’m hoping someone can help me understand this setup. The bike is a kuwahara caravan tour.