I started with an 80's Peugeot PFN10 12 speed, so it was an easy matter of finding a comfortable gear combination I could use for the entire daily commute. I ended with a 42/16, not much of a challenge, but quick in traffic, and low enough for some hills. I shifted the 42 to the outside of the spider with an extra set of ground-down bolts, and stripped all the other gears off the freewheel except the 16, which fits against the step on the freewheel housing. Alignment is very close to perfect. Added a single speed chain. Total swap, about 3 hours. A delightful ride.