Actually I'm considering doing the same thing. Except instead of a cassette, I'll be running a igh. It just hit me that it makes a lot more sense to recycle my worn out triple and get a 1/8 chainring than buy a cheapo square tapered Crankset that are way flexier than modern cranks. And it'll let me keep the bb standards the same between the bikes.

So quick question. Am I better off using the middle ring on my triple for optimal chain alignment with the rear SS cog?