We have made no tests with with N4373A and the 87075C, but in principle this should work. I recommend to use the mechanical switch version of the 87075C. However this configuration might not meet the original specification of the N4373A system.
If you need a users guide you can ask your local Agilent sales representative. The Agilent number for this N4373-90A01.
The Agilent LCA N4373A is not available with 75Ohm, but with a minimum loss pad you can adapt for 75Ohm. The N507X Network analyzer offers a procedure to correct for the measurement errors.