My biggest issue is that the stock crown is too small and recessed in the case. The original movement (7626) didn't support handwinding, but the NH36 does. The small crown makes hand-winding and setting the time and date difficult.

After some research, I found an auction archive for this mod that used a modified SNZG15 crown, machined to fit into the SNK809 case.

The Seiko part number is: 9K60ABSZW1

I don't have machining equipment, but I found the part here, for $10 plus shipping—cheap enough to experiment with.

I ordered two, just to be safe.

The Seiko part number is 9K60ABSZW1.

The parts arrived, and the finish looked like an exact match.

A rough fit demonstrated that the crown was indeed too large.

The SNK809 crown has a diameter of 3.9mm, while the shoulder of the SNZG15 crown measures 4.4mm.

Again, I don't have access to a machine shop, but I had a hunch that I could use a low-grit (#150) diamond file to remove the excess diameter. Instead of a lathe, I could use a power drill to spin the crown.

I attached the crown to a spare stem, wrapped it in some electrical tape, and put it in the drill chuck.

The drill direction was set so that the crown wouldn't unscrew from the stem. I used gentle pressure and slowly pressed against the crown's shoulder.

I paused occasionally to ensure things weren't overheating and to check my progress using measurements.

My diamond file didn't always have enough tooth to grind the crown, so I applied as much pressure as I thought was safe.

Still, the stem is very brittle and broke twice. But because of how I secured it in the chuck, it broke away from the crown, allowing me to use pliers to remove the stem from the crown.

After grinding down the shoulder, everything was washed to remove metal dust.

The new crown was fitted; none of the “machining” was visible, so I didn’t have to worry about polishing or bead-blasting.

The size and grip were greatly improved.

This is a side-by-side comparison of the old and new crown.