Buy a vintage Tropic rubber strap for that and get a signed buckle. Measure the lugs first.

 

Actually that model would have had a metal Bonklips bracelet. Here is a pic of it in a catalog

Here is a post on X (aka Twitter) that talks about it.




This would make sense as it would need a bracelet that expanded for a wetsuit.

It would look good on a tropical strap

 

IMHO, it does look good on the Bonklip as well.

 

I showed the watch to a local repairman yesterday, he said, "$88 to open the watch and no guarantees against damage." No thanks. I have the name of someone at a Longines retailer who I'll contact today to see if he can help. I can open the watch, but not without likely causing damage.
I have a no brand, tropical strap that I've had the watch on before, just trying to find its history.
I'll post an update if/when I hear from Longines.

 

After the past several weeks and a back and forth with Longines customer service, I received this,
"The original strap for this timepiece was a steel bracelet. Unfortunately, that specific bracelet is no longer in production and is no longer available. This is the extent of the information provided by our headquarters based on the timepiece pictured."
I sent them a response asking again, what type of bracelet this type of watch would have had? We'll see if there's a response as I stated that I would like to know, but didn't need to know, what specifically came with my watch. On another forum I also learned that the watch may have come with a JB Champion bracelet.
In other news, I contacted Jack A. from International Watch Works, as they last serviced the watch in 2004 and I sent the pics below. I thought that the markings inside the case back would have been from servicing, but wanted to confirm that, which he did. Their marking are at the top in the black "rectangle" with the date of 1/04. He said that they did not make any of the other markings which I'll presume are from previous servicing that my dad had done. There are both the additional numbers written as well as some engravings near the serial number.

 

An update and some whining. Just received an email from customer service and I'm pretty sure whomever responded had not read the previous emails. They again suggested I contact the Longines archives, which I have already done several weeks ago.
I find it interested and upsetting, that they either don't know or can't find, the type of bracelet that would have come with one of their iconic watches. And also, a watch that they thought so highly of that it was reintroduced.
It was a good attempt and thank you for the input here. It's going to stay on the nasty bracelet that my dad wore it on.

 

Bonklip is a fun strap imo