You'll be over 10:1 at liftoff with the smallest on M's, the AT M1297, at ~450lbf initial thrust. I'm assuming a 75mm motor tube?
Yes it’s a 3-inch mount. Right now my guess is that the first flight would be on an “L”. Once it’s complete and I have a final empty weight I can do the math and see if I can tolerate the C/G change with bigger motors.
If I do go with an “M” I’d use something with a gentler ride, like an AT M650, Hypertek M740 or a Loki M900.