In case anyone is interested, I did buy and try one of the freewheels mentioned above to see if the cogs fit an old body. It appears that they do not. The cogs have the proper diameter but the spline pattern is slightly different. The new cogs have one 'square' spline that is used to locate the cogs relative to one another. I did not check into grinding off the square spline.

In addition to the silver cog freewheels with the lockring to hold them together, I also found a later model Shimano freewheel with brown cogs and the small cog threads on to hold it together. These are not even close. The freewheel body is all one diameter (in between the small and large of the old style body) and the last 3 cogs are pinned together and only the small one of the three is splined and contacting the body.