The original non-integral fuselage tank is on drawing 32 in the current plans on CD that Van's sells.
I've not heard of an integral fuselage tank. Although I simply could have missed that, wouldn't be the first time, it's also possible that yours is a one-off. In any event, if it uses the firewall as a tank wall, I'd definitely replace it. I think it is essential to have some space between the firewall and any fuel.
RV-3B, now skinning the fuselage