Hi James,
The image here is of Hawk-Eye, which is known to be an early boat with a sail number below #150.
It appears to show an identical threshold plate to yours, with its narrowing slot which, together with a set of ferules, is designed to allow dropping the keel to various depths.
You'll see in the
Description Section that later Reedcraft and Moore's boats have a cast aluminium handle that sits neatly in a rubber sealed seating.
If it is
Tony Ayre's old boat, you'll need to confirm evidence of "the 2 non standard winches fitted in the cockpit" which I can't see in
your photograph and the "two large lumps of pig iron, fitted in a framework each side of the keel".
Possibly the picture of the
name on the bow would then settle it.