I had one of these freewheels back in the '60's. The 'picks' slide over the large sprocket and engage with the two recesses in the flange on the rear of the freewheel body. This locks the body as Jonny69 says and you take the block off with a chain whip. I bought the freewheel as you could fit a...
I also have bought kit from Hilary Stone over a period of several years. The purchases were always delivered promptly and matched the description and illustrations on Hilary's web-site. Like OSK I checked availability, price, shipping and payment before confirming purchase.
Chris.