Although I think you'd be happier with a 5 foot cutter, since you have a 6' unit, it can't hurt to try it.
As others wrote, you may experience the "tail wagging the dog" especially if you transport the cutter raised on the 3PH.
You can minimize this by making slow, more gradual turns...this, BTW, applies to both mowing and transporting.
If you do transport raised, keep the cutter low. There's no need to raise the cutter the full height of your 3PH...just get the tailwheel off the ground a few inches.
Also, rather then raising the cutter, you can tow it using the tailwheel to bear some of the weight. I've done this...just disconnect your top link.