I would not say that a WDH is necessary to be safe. Towing a 22' Funchaser with a 3/4 ton truck is probably OK without a Weight Distributing Hitch (WDH).
Here's a good guide to choosing the correct height ball mount:
Choosing the Correct Ball Mount | etrailer.com. One thing that the article does not consider is the sag on the tow vehicle as a result of the trailer being hitched. You can approximate this by measuring the hitch height with your current ball mount before and after hitching the trailer up. The amount of sag can be added to the ball height computation.
Make sure that you take a couple of other things into consideration: 1- Hitch capacity - this is often on a plate or sticker on the hitch. Make sure that it can handle the gross weight weight of the trailer (I believe that it is 5000-5200 lb) and the tongue weight (10%-15% of the trailer weight). Often there are two capacities listed depending on whether a WDH is used or not, 2- Hitch ball capacity - the ball rating should be no less than the trailer gross weight. Ball capacity is usually based on the diameter of the ball shank, and not the diameter of the ball. The capacity should be clearly stamped on the ball.