Denso Motor with CIMple Gearbox

[JellyMan]

We are considering using the Denso window motors and CIMple gearboxes to pivot a long lifting arm. What is under the plastic drive sprocket on the motor? If that piece is carefully cut off, would that leave a usable shaft which we could attach some kind of coupling to the CIMple gearbox? If this is feasible, does anyone have a recommendation for this coupling?

As we are unfamiliar with lifting arm and motor/gearbox calculations, could someone double check our concept? We have the following:
_ 65 inch arm of less than three pounds
_ 12 oz game tube (0.8 lb)
_ 2 Denso window motors (10.6 Nm stall) on each side of the pivot shaft
_ Each motor driving through a CIMple gearbox (4.67:1)

The JVN-DesignCalc spreadsheet seems to indicate that this would work, but I know the answer is only as good as the input assumptions!
Thanks.
Jeff