it is always advisable to get alignment after replacing front end parts. remember, these cars were never even close when it came to production tolerances to start with, so if you swap spindles to the later, taller, style [F,M,J body] that will certainly alter your current settings.
if it were me, i would swap to your discs now, then get it aligned.
i don't know what you have decided on discs yet, but don't fall for the 73-76 A-body "is the only setup to use" story. the later, [3/8" taller] F,M,J body spindles WON'T cause alignment problems or overextend the upper ball joint, causing failure. if you are using an aftermarket kit, i would check the master cylinder size so you get the correct size for your intended use. our good DR. DIFF will set you up with an outstanding kit with the CORRECT size master, so if you have nothing now, contact him first !
just my experience and opinion from playing with this junk since 1959. your mileage may vary.......