Here is my question. I have 2 shimano freewheels. One is an old Shimano 6 speed, the other a newer Shimano 7 speed with the better stepped cogs. Is there any way I could take 6 of the new cogs and transfer them to the old freewheel?

I had the freewheel fixtured in a vise between 2 planks of wood (not to damage the cogs). I tried to remove a cog on the old Shimano freewheel using a chain whip. I could not get it to budge.

I know the easy answer is just to buy a new freewheel... But I read that people used to switch out cogs on freewheels.

Help? Suggestions??