I spent the day compiling stats
Free - older style (like older VS machines)
Gap .127, height (exterior) .50, gap to needle hole, .425, needle hole offset to right
New Royal
gap .127. height .523, gap to needle hole .475 with toe open - right offset - this set is also called "universal" since it has an larger, open ended needle "hole".
Free/New Home (newer style)
gap .127, height .70, gap to needle hole .50, center
The big different in these is the gap to needle hole measure, though it can be difficult to measure on the foot. I measured this on the machine - from the front of the clamp to the needle.
I'm sorting and getting things figured out and then will offer the rest for the cost of shipping. I counted, I've got over 60 sets of top clamp attachments, though I expect I'll be keeping well over half of them.
These are what I've got that are all different
Free - older style
Free /New Home - newer style (VS and Rotary)
New Royal
White (VS and Rotary)
National -older style
National - newer style (VS and Rotary)
Davis
Eldredge (pre National)
Foley & Williams
Standard (VS and Rotary)
New Home (pre Free)(VS and Rotary)
Household
And - I have at least two sets that don't quite fit any of these machines.
Side clamp are so, so much easier to deal with!