7073B R Replacement

I'm looking for replacement for 7073B R. I also need the left hand version. I've read the blog posts, and it seems like 39-094 is a good bet, with the track mounted under window casing. But, the arm is much shorter than the 11 inch arm on the original 7073B arm which is 9.5 inches. Is that difference in length ok? And, it seems I will need to modify the wood trim part that goes over the gear housing will have to be modified, which is ok. Thanks for any help you can provide. And see pics.