I too have Crohn's, but it's located in my terminal ileum. From the research I've done, I don't think there's a specific probiotic for a specific area of the bowel. There are so many different types and strains of probiotics out there, and it can get very confusing.
However, it is my belief that Bifidobacterium Infantis is more helpful than Lactobacillus. When I asked my gastro about any benefits of taking probiotics such as Lactobacillus, he instead gave me samples with Bifidobacterium Infantis. I don't think that probiotics have been PROVEN to help, but they MAY be helpful. I would suggest looking for capsules at your local drug store (supplements section) or health food store, and reading the ingredients to ensure its content. Good luck!
According to the pamphlet that came with my sample probiotics that the gastro. gave me, by 7-8 weeks the body should be experiencing the full beneifts. Of course, you'll need to continue taking probiotics if you decide that it's helping.
Hope this helps.