im not clear myself mate, but i have three racks here, my original early 88 rack and two alleged 90 spec racks. they all have that 84 number but also they have a cast mark like this

and apparently the early ones have a lock to lock of 3.5 turns, where a later september 88 onwards rack has 4.25 turns. so i may well have 2 90 specs and my original pre 88 spec, i just need to see someone elses original rack number on a post 88 car