Can I convert my externally balanced Big Block Chevy Fluidampr, into an internally balanced Chevy Big Block Fluidampr?

Yes, there are ways to do this. As there was a design change, you must first determine which type of bolts you have mounting the adapter hub to damper ring (see picture below). If the bolts are the new style, socket head cap screw, then you will need to replace your existing adapter hub with an internal balance adapter hub, part # 100001. If the bolts are the old style, flat head cap screw, then a replacement adapter hub is no longer available. However, machining the counterweight off the adapter hub will make it an internal balance damper (this should be done by a qualified machinist or engine builder).