I was wondering how you arrived at your grandpa being from the 29th? The 29th was indeed stationed in Cornwall before the D-Day invasion. I happen to have a book called "29 Let's Go: A History of the 29th Infantry Division in World War II" (originally published in 1948), which has a list of all soldiers of the 29th who were killed in action or died of wounds.
The closest matches I can find to your grandfather by unit are:
29th Signal Company: White, William W
115th Infantry Regiment: Waits, Jace M White, George E White, William N Whitehead, John P Whitman, Leo R Whittington, Jack E
116th Infantry Regiment: Waite, Richard A Whitacre, Ozro T Whitaker, Herbert C White, Gordon H White, Ottis A White, Peter J White, William A Whittaker, Jess S
175th Infantry Regiment: White, James A White, John E White, Leland O White, William T
Thats everyone whose name is White, Waite or something close. I also looked at Wright, but saw no Francis or one with middle initial 'F' or anything helpful.
I don't know if you have any experience with these divisional histories (most divisions had one written after the war), but my experience is that all in all they are a good way to get a lot of details about the particulars of troop movements and such during battles that are too detailed for most history books, since these books focus only on one division. That does not mean that they do not have errors or omissions (this wouldn't be the first time I've come across one). Considering that the 29th ID has something on the order of 3500 troops killed in action, I think it is very likely that some have been left out by mistake (and probably a few names of people that weren't killed as well), along with plenty of mispellings. Perhaps one the Whites listed above really had a middle initial 'F' for Francis and went by that name rather than his first name. Typos like that are a definite possibility.
So, if you have a very reliable source that says that Francis was in the 116th infantry regiment of the 29th infantry division, then I would trust it. However, if your source is perhaps not so reliable, then my suggestion is to consider a few other options (but not to rule out the 29th). As a further suggestion you might consider the 2nd or 5th ranger battalions, which were both attached to the 116th infantry regiment for the D-Day landings. Both would also have been in Cornwall at some point prior to D-Day since the 116th regiment embarked from various ports there for the invasion.I don't have easy access to casualty lists for these units or any other that participated in D-Day (other than the 29th of course) - I'm not even sure where the best place to look for them would be.
According to my book, the 29th division was stationed just outside of Salisbury (minus the 115th regiment which was near Oxford) in October of '42. In May '43 the division movedto Cornwall - the 115th regiment in Bodmin (hmmm....), Launceston and Bakehouse; the 116th regiment in Plymouth and the 175th regiment in Exeter; with the artillery spread all around.
I hope I helped some....let me know if I can help some more.