G'day Duncan,
0.81mm = 32 thou". Should be OK, just check the position of the tappet adjuster at 1/2 lift. It should be in line with and center of the valve stem. Thicker will move it in, thinner out. But not that critical on a road motor.
As Trevor said, they must be annealed properly, heated to red and quenched.
Cheers
