To start, welcome to this site! That 1976 CAT is a D4D. They made them from 1966 to 1983. PS means it's a 3-speed powershift transmission with a 3304, 425-inch, 75 HP, 4-cylinder diesel engine.
TractorData.com Caterpillar D4D tractor information www.tractordata.com
Manual-wise, CAT is very strict. You'll have to pay for them, but they can be found on Amazon for a low dollar fee.
Thanks, Charles. Even the TractorData says it's a 350 CI engine. It seems a lot of info is inaccurate.
Cats are odd; it all depends on which country they went to and what model from A to K. Personally, I would talk to a nearby CAT dealer and ask for help with what you need. Good luck.
Thank you. 1976 isn't that old; they should have manuals available still.
Is this the correct one? Caterpillar D4D Crawler Factory Service Manual