The R179 should replace all R32s and R42s, and I believe that some will displace some R46s to the SIR. After all, has confirmed that some R46s will be overhauled for the SIR.
Here are the line assignments for the B Division I would expect after all R179s are delivered:
R46 - , , and SIR
R68 - (, , , and
R68A - (
R143 -
R160 - , , , , , , , and
R179 - , , , and
In this way, Jamaica goes all R160 where the and give up their R160s to the , , and , and the new R179s are assigned to them. Considering the and got shafed in the R160 order, I wouldn't be surprised if it happens again.