Hi rayray,
The bolts won't be metric ,more likely Whitworth or SAE.
Yes the pivoting alloy carrier could be alloy welded.
It's best to remove the bottom blade off the base plate for sharpening.
There doesn't look like a lot of room to get a socket on that nut ,you may need a tube box spanner or
use a blunt chisel or pin punch or centre punch to try to undo the nut .
Cheers
Max.
