30-06 barrel locking spring
If your 1919 was built properly, the rear .308 spacer should be held in place by the 4" retaining pin that runs longitudinally below the left side feed area. Pull this pin and remove the .308 front cartridge stop and .308 rear spacer. Reinstall 4" pin to retain the belt holding pawl. Under the front .308 cartridge stop, you should have the stock 30-06 cartridge stop. Replace barrel, booster, and install a USGI barrel locking spring. The barrel locking spring must be replaced due to the different shape of the locking notches in a USGI 30-06 barrel vs. the Izzi .308 barrels.