Do you have any photographs of your pump?
The range of manual pumps is shown here:
https://www.whalepumps.com/marine/produ ... ilge-pumpsI don't think Whale has changed the design of any of their traditional manual pumps - the Mk5 and the Gusher 30, for example, have been the same for 50 years or more. The Mk5 deckplate has changed, but both old and new designs fit the same pump. I recently fitted a new Mk5 to replace a Mk5 that was fitted in 1981.
[Actually that was removing a Jabsco bilge pump that had been fitted as a replacement for a Henderson (now Whale) Mk5, so that I could use the same hole for a holding tank pump out]