Just thought I'd throw something in here.
I am not completely familiar with the belt tensioner set up for the 414MII but is it really necessary to add an extra one?? It is actually better to run your car with no tensioner as your drivetrain will work better.
Unless your belt is skipping then I would say don't use one. They just add another point of friction in the drivetrain.
Belt drive cars are actually more efficient at full speed when the belts rise off the pulleys slightly therefore creating less friction.
A tensioner usually prevents this to some extent.
So in the end unless you really need them to prevent skipping the maybe do without them.
Just my opinion