Hemphrey, your choice of sizing material intrigues me. Why are you thinking of guar gum? I've never heard of anyone using it for a size, but that doesn't mean I don't think it would work, it just means you may need to do the legwork yourself as far as experimenting with it. And what process do you want to print on the sized paper? For gum printing, gum arabic can work as a size if it's crosslinked so so as not to be soluble in water. Some people mix it with dichromate and expose it to light to crosslink it; that's more trouble than I want to go to and I crosslink it by mixing it with glyoxal when I've used gum arabic as a size. Not being familiar with guar gum I have no idea how similar it is to gum arabic in structure, solubility, or how well it crosslinks as a dichromated colloid or with a crosslinking agent like glyoxal, so it's impossible to tell you how to use it as a size, sorry.
Katharine