Hi, I am A. Stevens here to help with your question!
This belt kit should work for you
You may want to specify to the seller that you have a CT300
and not a CT320
he should have it available
Here is another seller
Hi Steve, just ordered drive belts from Vintage for CT300. Apparently the 320 etc will not fit the 300 series. however thank you for your prompt reply and information. I envisaged scraping my loved CT300 which is 35 years old. thanks once again for your help.
Kind Regards David.