Whilst it's great to find you can save £9.50 if a digital version is available, this was not an option in the past and still only applies to certain periods for deaths and births - and not at all for marriage certificate copies.

Unfortunately, it looks like you will have to fork out and make the full payment, as I'm unaware of any other means by which you will be able to find his precise date of birth. Oh….unless he left a will - in which case you will be able for find the date for free on the Find A Will website. I just checked there, however, and didn't find a probate record indexed for him in the 1965-67 period. You might want to check yourself as it is quite late and my tired eyes just might have missed something, and very occasionally probate might not be granted for some years after the death.

As a general point, it is always worth trying this means, especially if it is just the actual date of death that is required.