Connecting Block and Traveler on '82 Hobie 18

Hi, first post here, so please be patient.

I recently bought a used Hobie 18 (used to sail them with my grandfather) and think that I might be missing a part. Here's my question: How do I secure the ratchet block to the top of the traveler car? Do I need a specific shackle?

Thanks in advance.

It's not a specific shackle, but it should be stainless steel and it should be fairly heavy (the pin is probably 3/16" dia.). Basically, the shackle should be as big as possible while still being able to pass through the hole in the top of the traveller car and the pin must be able to pass through the hole in the bottom of the main block.

sm