Here are some bits from the darkest corner of my workshop.
This picture shows the small two part clamps on the frame.
The female part of the ball joint with the plate is OK.
There are two male parts of the ball joint, one has a 3/4" threaded end the other 7/8".
I only have sidecar chassis clamps with a 7/8" hole, but in two chassis tube sizes, 1 1/8" & 1 1/4".
The two small two part clamps sort of fit the bike frame but I think they might need some fettling as Jon rightly says, it would be a shame to damage your frame.
It may pay you to look for some better parts but if any of this is any use to you Email me and I will find out how much the postage will cost.