Help: Exp pedal for hammond XB-1

[texasflood_dk]

I need an expressionpedal for my Hammond XB-1 organ.
But buying a Roland EV-7 expression pedal is quite expensive.

Instead my idea is to buy a cheaper pedal to get the housing, and then modify it electrically to suit my organ.

As far as I know most inputs for expression pedal, only needs a potentiometer.
So the concern most lie how much current the inputvoltage source can deliver.

Does someone know what size (ohms) the potentiometer is inside a Roland EV-7, or better - what the desired potmeter should be for an expreesionpedal for a Hammond XB-1 ?

Cheers

Texasflood_dk