Riveting 623 Coupler

No washers on my 623 and the rivets looks original. Is Carl's tool the one based on a center punch but with different tips? If so, I just use a standard center punch (same tool, different tip) to start spreading the rivet. The coupler has to be firmly supported from underneath (normally the top with the engine upright) otherwise you will break the coupler. 

Pete

What part did you purchase?
Do you have a cast coupler assembly already mounted to it's bracket, or the cast coupler assembly only?

If it is the cast coupler assembly only, there is no separate rivet on the original part. The "rivet" is actually part of the casting of the coupler body.
The bracket has a hole that slips over the rivet. The bracket is then surrounding by a pocket molded into the casting.

I looked at a few spare assemblies in my parts bin. Two of them had the "rivet" along with the edges of the pocket upset with a single slash. It was as if the slash was done with a cold (metal) chisel.
One of them had two slashes.

There is no washer.

In my experience, those upsets (slashes) along the edges of the coupler pocket are import to the strength of the mount. Without them, the coupler will loosen and come off quickly.

Forgot to mention this tip: however you secure the new coupler, you will need to support the head while riveting or staking.
I find that a piece of felt placed between the coupler and your anvil will help protect the finish / details on the top of the coupler. If your "anvil" surface is flat, you might want to fold the felt over once or twice, depending on its thickness.

Thanks

This is the complete assembly with the bracket attached to the coupler coil.