Hi Paul,
Welcome to Chinook ownership! Glad to have you here on the forum.
I have a Concourse with the manual step, and I do tow (one reason I wanted the manual step, although the electric is luxurious, I imagine). My manual step does not require as long a drawbar as yours, but it is still a longer than normal one. I had to look around to find one, but was able to do so, and now have three of them with different drops, for various trailers. I always carry at least one with me, after one time in Wyoming where I unexpectedly wanted to tow a trailer for someone and COULD NOT find a drawbar that worked (I didn't have mine along) (side note: we solved it by him towing the trailer and me towing his toad car for which the drawbars are customarily fairly long).
Anyway, what you likely need is an "extra-extra-long" drawbar. When I was looking they were actually easier to find than the long-but-not-extra-long size my Chinook uses. These don't technically reduce your capacity, but they actually do in a different way. What I mean is, it's not the hard 50% of the extensions, but just by virtue of lengthening the distance to the rear axle, if you have tongue weight (trailer vs. toad) then you may run up against rear axle weight rating.
You can look for a certain "hole to hole" distance from the pin hole where it gets secured to the hitch, to the hole where the ball goes. However that may vary slightly if you have a rise on your hitch (I run mine with a slight rise to make my tandem trailer level, and the way that comes around the step makes it fit differently than if I were running a straight bar).
I believe the Concourses at least came with a special extra-extra-long drawbar, but maybe yours has gone by the wayside over the years. Here is one you might consider (maybe someone else with an electric step who still has that stock drawbar can measure it for you).
Here is a link to one extra-extra-long drawbar. This is about the same amount of rise I use for a trailer that wants the top of the ball around 19-1/2" off the ground (tandem trailers like to be towed as level as possible), although I don't use the extra-extra long with the manual step. Also, of course it may vary due to Chinooks not all having the same amount of perkiness at the rear step.
https://www.etrailer.com/Ball-Mounts/Hi ... 80233.html
Note that one of the zoomable views has a tape measure set alongside it (e-trailer is great for that sort of thing).
One other thing (that you may already know about) that can be put into the equation if leveling is important to you: You can get hitch balls with a riser built in (1" for sure, maybe more also). This can help if you are "between rises" and want to tweak it to be just right. May not matter for a single-axle trailer though.