I have used an aluminum drift with a pilot turned on the nose to prevent the drift from slipping out of position (at a slight angle in an SKS chamber). Some penetrating oil and perhaps even heat my be needed prior to applying a 2 lb hammer.
The receiver was protected by shaped aluminum blocks lightly clamped in place. A large (6 inch or more) size vise restrained this assembly. Don't forget to remove the small barrel cross pin.
The Chinese SKS barrels are a nominal 19mm diameter at the breach like their AK barrels. I just measured one at 19.05mm.
A friend has successfully rebarreled SKS's to .223 cal after we had been told all sorts of horror stories and BS. I believe that the Chinese SKS receivers are castings. Others may be also.
Are you changing caliber on your SKS ??