I suggest a M300 scout, I have a 8" KMR-A rail, so I know about how space can be precious. I got an offset mount that attaches at the 9 o'clock position, but puts the light in a 11 o'clock position and as far forward as I could. This puts it forward enough to not take up rail space I need for my support hand as well as having very minimal barrel shadow, but back enough that any shot residue can be taken care of with a clear lens filter (easier to clean, protection for my lens, and better to replace a filter than whole LED head).
I built my 300blk for HD, being light, compact, and sleek (very little to snag on things) was my goal. I have a 9" barrel with the previously mentioned 8" KMR-A. With a short rail, if you run back-up sights like I do (T2 batteries can, and will fail) then having as much sight radius is worth not mounting at the 12 o'clock. If you want a FDE M300 mini, Surefire had them in the online store recently and I'm sure you can find a used one somewhere.