answer-
when the chain exits the freewheel the angle is so great that when the narrow link dis-engages there is a noticable "shift" to chain,
yes it may work, but you cant pedal backwards as the chain jumps over the cog.

Question-

I was thinking simmilar to your concept on building a custom freewheel.

I have a few 7 speed shimanos from MTB's and could look into creating a shimano narrow 6.

Please post some pictures and text of this as I am highly interested in conversion