There are some designs that were made LSA-legal by reproping. The thing
is, they were just a few knots off... the RV3 is like 50Kts over, isn't
it?

Personally, I suspect that such a plane would be a troublemaker. By
putting a grossly wrong prop on it or swapping out the engine you may
create a legally LSA-compliant plane... but people know what an RV3 is.
When you say "LSA-legal" they are going to say "prove it".

Other than that... is the listed stall speed clean? LSA says 45Kt Vs1
(no flaps).