Wasted some more time searching. Nothing good ...

I found one source for #3676478:
Collectors Auto Supply $3.00 ea Part numbers listed in order
Description says "Clutch Head Bolt" and does not mention the lock washer. The diagram in the FAM shows a hex head bolt.

Other info:

#3676478 BOLT ASSY w lock washer 5/16-18 X 1
Shown on Sect 11, Sheet 20.00 1947-1954 FAM
'29-'54 MPC Group 8.206 Part 3676478
GM Parts Wiki 1
GM Parts Wiki 2
Chevs of the 40's lists the part number, but it is not the correct configuration

- Lonnie
My '54 3104
Photos that I have shared on Stovebolt via PhotoBucket are no longer available. Please contact me if you want a photo from an old post.
lonniecook [at] aol [dot] com. I sold my '54 3104 12/12/2017, but I still visit Stovebolt.

OLD STUFF ... houses, furniture, cars, wine ... I love it all