I am not sure what clearances your engineer was refering to, but do I know that both the SCXI-1128 and the 4060 have been thoroughly tested up to 250Vac. As long as you're careful not to sink more than .8mA across the SCXI-1128 you should be just fine. Also, if you are routing your signals to the High-Voltage Analog Bus on the back of the SCXI chassis, you need to make sure that you don't have any other modules connected to the bus which have a lower voltage tolerance.