Hi Borobike;

I am very glad you like the dual pivots. Your experience is the same as mine

A note on freewheels - the minimum number of teeth is 13. Seven speed freewheels that I know of with 13T in the smallest cog::
Sunrace 13-28; uses Park FR1 (Shimano) tool; Amazon (put one on the hybrid I just sold to a friend; I rode it about 500 miles, no issues at all.
Shimano 13-28; Amazon
Sunrace 13-25; uses Park FR1 (Shimano) tool; eBay; currently on my commuter.
Sunrace 13-24; uses Park FR1 tool; Harris
IRD 13-24; Harris
IRD 13-28; Harris
IRD 13-32; Harris
http://www.sheldonbrown.com/harris/freewheels.html#7

The IRD ones are really nice, and expensive too.

I just ordered at Shimano 13-28 (13-15-17-19-21-24-28) with an idea to take it apart, and combine with parts from a Shimano 14-34 (14-16-18-20-22-24-34) to create a 14-15-16-17-18-20-24 or similar with one tooth steps in the upper range.

Sunrace seven speed freewheels are about 2mm wider than Shimano seven speed freewheels - probably not an issue for your bike, but was for my mid 80's Suze-Araya wheel

To go to 11T; you need a modern (8 speed) freehub and cassette.

This wheel would do it for you: http://www.amazon.com/Mach1-EXE-Rear...0176636&sr=1-3
it has DT spokes, so at worst typical maintenance (tension/true/stress relieve) and greasing the bearings would get a wheel that would last a lifetime.

Then you'd want one of these" http://www.amazon.com/SRAM-PG850-Spe...0176757&sr=1-5

etc