Best RV3 Guy at Vans...Modified wings are not "B" wings.
Try to get to Phil. He seems to be the most knowledgeable.
My understanding is that you can not upgrade old wings and make them "B" Wings. Depending on vintage, there are several modifications to the old wings and fuselage that can be done to strengthen them, specifically at the wing root and rear spar cross over mods in the fuselage. They are still not "B" wings as the spars and general construction or different, not to say they are not as strong, I dont know, just not the same. A modified wing is different than a "B" wing.
Or, you can order new "B" wings and refit a new center section into the fuselage. You still have to make the necessary fuselage modifications to the rear spar carry through as well. Then you have wings tanks and a fuselage tank to deal with.
I looked at buying a built 3 and modifying it. I ended up with a new kit due to all the variables and variances of the older 3's. Everytime I found one, there was something a little off about it that scared me away. If I already owned one, it might have been a different.