I’ve decided to get a triple crank for my 7 speed freewheel, so I’ve been looking on Ebay and Craigslist for the usual – Sugino, Sakae, Takagi, and Shimano FC-6206 with 110/74 bcd. I am finding plenty to choose from, but none of them have the exact combination of chainrings I want: 50 outer, 34 or 36 middle, 28 or 30 inner. Most have the 28 or 30, so I would need to replace the outer or middle, and searching for an individual chainring has proven mostly unsuccessful. It seems there aren’t many used ones out there, and the new ones are about $40 on up.

Today, it occurred to me that if the triple I end up with has a 28 or a 30, but not a 50 outer or a 36/34 middle, maybe I could use a chainring off of my current Shimano Claris 50/34. to swap outer or middle. My Claris is 5 bolts, 110 bcd, so either chainring should fit as a replacement. I know Claris isn’t top of the line, but other than that, and maybe looks, are there reasons anyone would recommend against this?

Or, could I get triple crank arms, use my Claris 50/34 chainrings, and then buy a 28 or 30 chainring?
Thank you, in advance, for your advice!
Brian