you need to find a 4wd set of rollers

if you remove the front prop you'll get no drive as you need to have everything connected in order to transmit power

the viscous coupling is like a diff with the viscous in the middle so you will essentially be apply power which the vc will tr to direct forwards as it thinks the rear wheels are slipping
this will last you perhaps 1 mile before you lose all drive because the vc will be trying to sepnd power to the front wheels but because it's burnt itself out there will be no drive anywhere

the reason that the car keeps on going when the vc has failed in normaly use is that the front wheels are turning anyway so it doesn't detect any slip so it does nothing, and even when it does it can't send power there so it all goes to the rear, but it's behaving like an open diff then, so if it's an open diff when it's failed you will get no drive at all

hope this clears things up