No can do unfortunately 
I tried 
And I agree. The somewhat low stack is the one reservation i have about it, but i also know i can work around it.
The 35C though is confirmed, and it's a huge positive.
Edit: bike fit shenanigans, in case it's useful for others.
The one thing i wish were different on this FM126 is the stack: wish it were higher.
Who doesnt like trigonometry on a Friday?
I'm on a LTK268 M, so vs the FM126 in M, the 126 is 2mm longer and 8mm lower, which i dont love. I went from 80 stem to 100 on the 268. From 126 M to L, stack is up 21mm, reach is up 11mm, and seat angle is 0.5 degree slacker, which at my saddle height is 7mm further back, which i dont love either (I ride on the flat mostly so i slam my saddle fwd by default.
So, if i go from 126M to 126 L, you're up 21mm in stack, and 18mm in reach (11 + 7 from the saddle). If i drop back to 80mm stem, then i'm back to square 1, but i gained 21mm in stack. Which then allows me with a full spacer stack to be significantly higher (my saddle to bar drop is pretty epic). 268 M to 126 L is 20mm longer (13+7) and 13mm taller. So i can drop back down to 80mm stem and get an L. Also, they will be making a zero offset seat post, so i'll get one of these on top of the regular one. I'm going to have so much seat post exposed compliance wont be a problem, especially on 32C measuring 34-35mm. If i do that, i will be able to play with the "higher stack is faster when in tuck" vibe.
If you understand anything, bravo, because i dont.
I THINK that M to L in the 126 is basically reach neutral, you gain 21mm stack, and your hip angle should open up. Even more so with a 0 offset seat post. So I guess i'm leaning towards an L. For reference, i'm 184 and my saddle height is 80-81cm. I also plan to switch to 165mm cranks, which should open up my hip angle even more. Might be worse off in the mountains, but so much of my riding is on the flat, i'm solving for that.
Adding a 10mm spacer on the M should be close enough for you to make no changes. I think you are already doing this, but it's important to remember that adding spacers adds stack AND reduces reach. Because of this, the L is ~17mm longer than the M (if I am reading the sizes right) at the same stack height.
Your bike fit is super old school, so IMO the question for the L is more about whether or not you wanted to try a more modern position which would require more or less a total refit, as you likely need to change your saddle position for that size to work. However, I think that it would be worth it for you. Ideally, you could find someone with a bike that size to try riding with or get on a fitting rig and see how it feels, both JRA and when doing a hard effort.
