Will head and upper body shots show a lot of distortion?
That depends, you have to consider everything in photography from end to end, scene to print. You need the context of the final product to make the lens choice meaningful.
The distortion seen in wide angle shots and flattening seen with narrow angle shots are the result of a mismatch between "the camera taking angle" and "the print viewing angle".
For example a shot from a normal focal length lens (50ish lens for 135, or 100ish for 6x7) printed at 8x10 and held at a normal reading distance is probably going to look pretty normal to you.
Using a wider angle lens (say your 35 on your Leica) and printing 8x10 again and holding the print at the same distance you'll start to see distortion if compared to a 50, bigger noses etcetera. BUT, if you print that shot from your current lens at 11x14 instead and use the same normal reading distance the distortion goes away. Holding a smaller print closer than normal does the same thing.