Mod Wheel Modification

[skinny bastard]

Okay, contrary to my previous post, I am not going to have any problems 
adding a mod wheel to the roland 180 keyboard. However (and there is always 
a however, isn't there?), I do need some help in locating the equivalent of 
two parts listed for the circuit. What I am doing is just building the 
circuit for the mod wheel on the 181, and adding it to the 180. There is an 
an IC listed as uPC4558C and another part listed as SR19R. They are labeled 
on the schematic as VR6,7 and IC3. This is a link to the page that has the 
schematic: 
http://machines.hyperreal.org/manufacturers/Roland/System-100m/schematics/s100m17b.jpg
Any help would be appreciated!
James Tiller
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