Ralph,
Why all the toggles?

Can't imagine that the drum would interfere with the pullpit if it was lower. Perhaps who ever installed the furler measured incorrectly and cut the forestay a bit short, thus the toggles. Maybe you just need to remove one of those to shorten your forestay. Each toggle is also a possible fitting to fail down the road.
The threaded portion under your furler is indeed the adjustment as Graemek has explained. It is not a turnbuckle rather a one screw adjustment. Screw it in to shorten and out to lengthen. Be very careful to leave enough threads screwed into the furler so they do not part company. Theoretically you would be screwing the parts together, but if you choose to remove a toggle you may need to extend slightly.
Graemek also brought up a good point, your backstay (while the boat is at rest and not loaded) may not be carring the load. It could be your triasic stay (mast to mast) and your mizzen backstays.
I would recommend that you loosen what you need to loosen to get you mast straight fore and aft. Then determine how loose your forestay actually is. Shorten the forestay preferably by removing a toggle or two, and then tighten the main mast backstay to achieve the desired headstay tension. Sight the mast to make sure it is still straight, if not repeat the procedure. Once the main is straight and true, then you would adjust your mizzen so it is parallel with the main. You don't need to measure the parallelism with a ruler, just eyeball the rigs from a nearby dock. If it looks parallel it probably is.
As far as headstay tension, this one is a tricky subject. As a rule of thumb, I tension my headstay with the sail installed so that at the dock there is not any noticeable sag. You can deflect it slightly when it bounces if you push and pull aggressively but all in all it looks straight to the eye while rolled and unloaded.
You could also do the math by using your mizzen halyard. Measure the vertical height of the mizzen mast from a horizontal line extending from the butt of the main mast and then the distance from mast to mast along the cabin top and calculate the hypotenuse. Then use the halyard to hoist a tape measure and adjust the mizzen mast rake to the correct hypotenuse number. The eyeball method is all we use.
One other thought came to mind. Even though your backstay is split and the load on each lower leg is 50% of the total load, the lower wire size is smaller than the upper section of backstay because it only has to carry 50% of the load. So make sure you take the wire diameter into account with your tension gage if you go that route.
I would agree, the most typical reason a roller furler is resistant to rolling is insufficient forestay tension.
Dale