I just bought a set of 20mm offset clamps for my 07 crf450.It looks like the previous owner machined down the top clamp to accommodate a-kit forks.Does anyone know of a way to make the clamps work with my current 47mm forks?

If I understand this correctly someone has bored the hole larger where the fork tube is clamped?  If that is the case you can have shims or spacers made that are the same with and I.D. of the clamp and same O.D. of the fork tube.  Have a slot cut so the spacer will change diameter when the clamp is tightened.

Thats what I might have to do.
I bought a set of rg3 clamps off craigslist and the guy failed to tell me he had the clamps reemed out to fit a-kit,now it's my problem.