I have a couple more ideas....
Kenmoreman above is right - if the hold-down bar that sits above the two cam bars is not there or is loose, you will get a funny clunking sound which comes from the cam bars flipping from one position to the other too fast. I have not heard that but once or twice, but I DO indeed remember the noise. The "hold down bar" looks like a bow-tie sorta, and is usually black in color. It is there to dampen the knee-jerk, spring loaded reflex of the cam bars, so that is very possibly the source of your noise. Hopefully yours is just loose. If you don't have one I probably have a couple of spares.
A couple more thoughts:
Be sure there is enough grease in the cam bar tracks - WP recommends Rykon grease.
Also, check the setting and fit of the post (the basket drive yoke support) that rides on the spin cam bar and holds the far end of the clutch yoke (as seen from the service panel area. Many machines, especially models from the 70s, used adjustable nuts on that post and it could be out of adjustment, especially if you had to piece-together parts from various sources. I have noticed a distinct thunk or clunk in machines when the basket drive came together to go into spin if there was too much play in the basket drive yoke spacing. I have also noticed this, but to a lesser degree, when the clutch pads were severely worn.
One more note - Since your early 60s machine pre-dates the fast brake design by about 10 years, be sure if you're using a newer fast brake clutch, that you used a hardened spin cam bar and not the original from the machine. The pressure/force of the brake can deform older cam bars after while, and though I have never seen that happen, WP repair manuals warn about it, and I would think this could cause noises of varying degree if the bar is not operating properly.
Best wishes with the machine!!!!! Let us see some pics soon if you can.