I posted a photo of a JDQA fork carriage a while back with measurements written on it, but I can't find it now. I have it on my home computer though and can try to post it tonight unless someone beats me to it.
The hooks are available from JD, probably more efficient to buy them vs fabricating. The hooks vary by implement maker, there's no exact standard for width or style. What do you mean by offset? The tilt of the attachment is determined by the lower pins and varies by type of implement. I believe radius is 1 or 1.25", but no longer have any QA parts I can measure.