I too was scared to contact professors in history programs. What helped me actually do it - and I'm grateful that I did and have been - was to think that they're probably getting tons of similar emails from prospective students. So it can become (or at least I convinced myself of this) win win: if your field is a bad fit for them, they'll say so and will either suggest others or forget about your existence; if your field is a good fit, then you have someone in your court when you do apply. Or the midline: if they're interested but unable to advise, you haven't really lost much; if they want more information, you have a great opportunity to build a more consequential relationship before applications are read; if they don't respond, chances are they won't remember you.
In any case: of the few professors I have contacted so far, all but one has expressed an interest in my material, offered substantial (like two pages) advice, asked to hear more about my project, and encouraged me to apply. The one who didn't offer positive feedback as explicitly (she did still offer some advice) is simply not going to be on campus when I will be, which is very helpful to know as well. So you really have nothing to lose, and TONS to gain.
I wrote the following:
-introduction (name, college, major, year, hoping to apply, etc.)
-BRIEF summary of interests - like 2 sentences
-BRIEF mention of their interests, and inquiry as to their availability on campus to potentially advise or advice on some content-related topic
-closing (if you'd like to know more, email or phone, etc.)
and write thank you notes if you get real substantial replies! They don't have to offer that kind of stuff, so showing your appreciation for the time they took to offer assistance will not go unnoticed.