"Anyone know for sure what size flax the 6V92 stuffing boxes use on the drive shafts? Looks like 1/2 in."
Only way to know for sure is to measure. The simplest is to take loose the crush nut and use the back end of a drill bit to see what fits.
Duramax or similar has replaced flax for a couple of decades.
No required leak underway , no drip when stopped and usually adjusted once after installing.
Duramax Shaft Sealing Systems: Ultra-X High-Performance Packing
Ultra-X lasts over 5 times longer than other packing
. Ultra-X is a high performance, non-asbestos, compression packing
that is engineered specifically for the marine industry. ... Unlike flax and other packing
materials, once Ultra-X is installed you never need to worry about ...