The conversion is very simple.........and you may only have to use a 2-pcs. Blank-Barrel-Assembly and try different "restrictors" (dependent on the Blanks that you will be using and the outside temp.) to make an M53 fire 7.62x51mm/.308 Blanks reliably.
Have you looked into the "Blank-Adapting-Section" at the bottom of the MG42-Section (?)........lots of information in there.
US Army, RET