It is perfectly fine to shoot 1.75oz loads thru a .655 Jellyhead choke. If you decide to go to heavier than lead loads you may want to go with a .660 or larger choke so you do not experience a blown pattern.
I am not sure what you read in the owners manual, but your gun is more than capable of shooting loads larger than 1.75oz. The best pattern I have gotten out of the Stoeger 2000 was with Hevi-13 3" 2oz #6's.