I haven’t done any research, can the block be removed or does it have to be re-barreled.
The white plastic block is in the magazine, not the chamber or barrel, and it can be removed. CMP is a bit misleading when they say "to prevent the loading of a .30-06 round into the chamber." If you are loading directly into the chamber, only the short chamber itself will prevent you from getting it all the way in there as the bolt stops 1/2" from going into battery. In fact, you can use a .30-06 case to purposely hold the bolt out of battery for easier extractor removal on a .308 gun. You have to get creative (or, horrors, use the proper tool) on a real .30-06 gun.
This is a legal rifle for ViMSAR (3rd Sat at DSRPC) and the Vintage Military Rifle Silhouette match in Boulder City (1st Sunday). Awesome group of guys to shoot with, if you don't wind up in my squad.