I agree to use actual documentation to be correct. I would like to help with this in any way, but there are a handful of members/users that are very knowledgeable on various makes. MrCadillac is one such user for obvious reasons. Dealing with the hyphen issue, on my MoPar book Standard Guide to 1950s Chrysler there is not listed a hyphen for models up to 1950-1957. For instance S16 instead of S-16. If my book is not valid, I would appreciate finding a more useful sourcebook.
I will check with the Buick Club to which I belong on the LeSabre issue. RESULT: 1959 owner's guide shows there to be a space. Will follow up on other model years.

As far as DeSoto goes, there is no space between letters on the hood (otherwise it would look wierd), but I believe there is an actual space De Soto used in company documents. I often slide by writing DeSoto, but I will consciously make an effort not to make this mistake again.