[Bill Harris]

The RPM "pills" for the analog MSD boxes are just resistors and are relatively high values compared to the wiring. For example, a 4K pill is 2700 ohms while a 7K pill is 5660 ohms, nominally. Extending the wires won't add enough resistance to vary the set-points unless you use tiny gauge wire and/or make really bad connections.

One thing you should think about, though, is that "pill" is in a pretty high impedance circuit, so it is susceptible to electrical noise which could make the set-point jump around. If you do extend the wires, I would use a shielded cable with two conductors, perhaps an 18 gauge shielded speaker cable (foil shield is best) and ground the shield at the box end only.