Rear brake bias problems - Viper front calipers with rear drums

first that switch on the wildwood prop valve is a brake light switch ( not a warning light switch )
verify the lines are plumbed correctly threw that prop valve. you should be able to just about eliminate all rear braking when its turned in.
I have a similar set up on my valiant 11.75 fronts ( stock calipers ) and the wide 10" rear drums without any issues at all.