Just one persons opinion. 75-95 K, a pipe dream.
The car, outside the pro car world, would not hold a lot of interest, as indicated by the sales number. To me, not unreasonable.
In the pro car world, were it a true ambulance, it would command a higher price, purely because of the rarity. Try and find another 56 straight ambulance. What that number would be be depends on the buyer of the moment, and overall quality. The buyer pool however remains small, and the value will be impacted by this. I am fortunate enough to have a #1 57 Superior Pontiac straight ambulance, and paid significantly more, but it is a true #1 car. I feel extremely fortunate. I would do it again without a doubt, finances permitting.
If it is a combination, keep it that way, and represent it as such. The buyer pool however will remain small, with a sales value therefore only slightly higher, maybe 20 K.
A high quality restoration of a standard 56 Pontiac, which would have a much larger interest base, coupe 25-40K, a convertible, 40-60K.
Again, just one person's rant.