Nice set of 189s you got there
The Jointers that are already installed, as opposed to rolling Coulters, work fine in previously tilled fields. While you're searching for the Latch Bar assembly, you'll need to keep an eye out for some other parts you're also missing:
one (1) 513 988 R2 Lift Bracket assembly
two (2) 512 308 R92 Lift Links with pins
two (2) 3839 BA Eyebolts
The Lift Bracket is/are two identical stampings bolted to the rear rockshaft and catch the lift chains ; the Lift Links connect the Depth Adjuster arms to the Drawbar Eyebolts.
I'm about half way through reconditioning my set and was fortunate to replace some missing parts with NOS from the factory, thanks to my local dealer.
Good looking iron and here's wishing you success finding the missing stuff !