Sorry, I must be quick as I have a funeral quite soon. Bigmamma, I think that's a lovely idea. However, family, please check with the cemetery first as it may not be permitted. Some council cemeteries prohibit more than one stone..be it a header or footer.
I'm afraid, under the circumstances, there is little you can do. Your grandfather did not make specific wishes. His partner, by our laws today, still would consider her in making decisions, especially if there were a will in place. Had it been in a church cemetery, there 'could' have been some other areas to consider.
May I offer this thought. Whilst I realise the absence of the words you want are distressing to you, the senitments you wish to share with your Grandfather do not go unnoticed. Speak to him, share your thoughts. Be there!
http://bigworldsmallboat.blogspot.com/search?q =as+long+as+we%27re+remembered
You are in my thoughts
Fr Bill