Headshot overlay

Not sure if this answers your question! but-

Lightroom has an "Onion Skin Overlay" (View Menu: Loupe Overlay > Layout Image) feature that can be used in the Develop module as a guide to cropping.

Create for yourself (in Photoshop )  a template, (eg. an oval, or anything you desire)  with transparent background, and save as a .PNG file. (Suggest the same image ratio 4x3 etc, for the image as your camera files)

When editing photos in the Develop module apply this PNG image as an 'Overlay' to be a guide to your crops of portraits. [Ctrl+Alt+Shift+O] (locate the PNG file). The only downside to this is that the overlay disappears when you select the crop tool, but it reappears when crop tool is closed- to be used again?.

The PNG overlay can be any image- as long as it has transparency to see the image behind!

HINT: The Layout Overlay can be used in Loupe view when shooting Tethered. So in a studio you could be checking your camera framing of the Loupe view images as you 'shoot'. 

The crop setting is not one that can be chosen when defining a preset, unfortunately. And, as far as I know, the crop tool always defaults to the full-size image that was taken. I think about the simplest thing to do would be to adjust the first image and then move to the next and click on the Previous button. Doing so will apply the settings made to the previous image to the highlighted image, and that would include the crop setting. Of course, that would probably necessitate some adjustment being made to each image.